feat(config): create a new project's memory file from Settings

The Memory tab could only show this machine's user memory and the
dashboard's own project file. Setting up a project you had not run
through the dashboard meant opening a terminal — `PUT /file`'s
"project" scope always resolves against the server's cwd, on purpose.

Add one narrow route per tool that writes into the directory you name:
CLAUDE.md for Claude Code, AGENTS.md for Codex, both through the same
`project-memory.js`. Being the only write path that honours a
caller-supplied directory, it pays for that:

  - the directory must be absolute and already exist — nothing is
    created for you;
  - the filename comes from the route, never from the body;
  - an existing file, symlink included, is a 409 — this can only
    create, never overwrite;
  - it sits behind the loopback-Origin guard /api/run uses, so a page
    in the user's browser cannot plant agent instructions in a project
    directory. That guard moves to lib/same-origin.js to be shared.

The modal takes the dashboard's known project dirs as suggestions on a
free-text input rather than a closed list: a project it has never seen
is exactly the case this exists for.

Mutation-checked: dropping the origin guard, and swapping lstat for
stat, each fail a test.

docs/API.md

@@ -1587,6 +1587,7 @@ POST /api/cc-config/profiles/activate     Body: { name }
 DELETE /api/cc-config/profiles            Body: { name }
 PUT /api/cc-config/file        Body: { scope, type, name?, content }
 DELETE /api/cc-config/file     Body: { scope, type, name? }
+POST /api/cc-config/project-memory        Body: { dir, content }
 PATCH /api/cc-config/settings  Body: { scope, set?: { "dotted.key": value }, unset?: ["dotted.key"] }
 GET /api/cc-config/plugins/available
 POST /api/cc-config/plugins/install       Body: { spec, scope? }
@@ -1603,6 +1604,8 @@ POST /api/cc-config/mcp/remove            Body: { name, scope? }
 
 `GET /api/cc-config/memory` also surfaces the per-project file-based memory store — every `*.md` under `~/.claude/projects/<slug>/memory/` (the common pattern of a `MEMORY.md` index plus one file per remembered fact). Those items have `scope: "auto-memory"` and carry `project` (the `projects/<slug>` dir name), `name` (filename), `isIndex` (true for `MEMORY.md` / `INDEX-*.md`, which sort first), and parsed `frontmatter`. They are **editable**: `PUT`/`DELETE /api/cc-config/file` accept `{ scope: "auto-memory", type: "auto-memory", project, name, content? }` and create a timestamped backup under `<memory-dir>/.cc-config-backups/auto-memory/` before mutating (an invalid `project` slug returns `EBADPROJECT`). `GET /api/cc-config/backups` lists these with `scope: "auto-memory"` and `project` set. Bodies are also readable via `GET /api/cc-config/file` (they live under `CLAUDE_HOME`).
 
+**`POST /api/{cc,codex}-config/project-memory` (a new project's memory file).** Creates `CLAUDE.md` (Claude) or `AGENTS.md` (Codex) inside the directory named by `dir` — the one write path that honours a caller-supplied directory, because bootstrapping a project the dashboard has never run in is impossible from a writer pinned to the server's own cwd (which is what `PUT /file`'s `"project"` scope means). It stays narrow: `dir` must be absolute and already exist (nothing is created for you), the filename comes from the route and is never taken from the body, and an existing file — including a symlink under that name — returns **409 `EEXISTS`** rather than being overwritten, so this endpoint can only ever create. Bad or missing directories return 400 `EBADDIR`. Unlike the other config routes it sits behind the same loopback-`Origin` guard `/api/run` uses (403 `EBADORIGIN`): a page in the user's browser could otherwise plant agent instructions in a project directory. Returns `{ file, size, created: true }`, where `file` is the realpath'd target, and broadcasts `cc_config_changed`.
+
 **`PATCH /api/cc-config/settings` (key merge).** `scope` is `"user"`, `"project"`, or `"project-local"` (`settings.local.json`). `set` maps dotted key paths to JSON values; `unset` is a list of dotted key paths to delete. The server re-reads the target file **unredacted**, applies only the named keys, backs it up under `<dir>/.cc-config-backups/settings/`, and writes atomically — so keys the UI never displayed (including secret-valued ones) survive byte-for-byte. Returns `{ path, backupPath, created, changed }`. Hooks are edited through this same route, as `set: { "hooks.PreToolUse": [{ matcher, hooks: [{ type, command, timeout? }] }] }` — i.e. `settings.json`'s own nested shape, not the flattened shape `GET /hooks` returns. Errors: `EBADSCOPE` (unknown scope), `EBADNAME` (a key segment outside `[A-Za-z0-9_$][A-Za-z0-9._$-]*`, or `__proto__`/`prototype`/`constructor`), `EREDACTED` (400 — the payload contains the `<redacted>` placeholder, which would destroy a real secret), `EBADJSON` (409 — the file on disk is not valid JSON; it is left untouched rather than clobbered), `ETOOLARGE`. The project layers always resolve against the **server's** cwd; `?cwd=` is honoured on reads only, never on this write.
 
 **Plugins and marketplaces.** These five endpoints shell out to the `claude plugin …` CLI with an explicit argv array (never a shell string); mutating calls are serialized in-process. `CLAUDE_CONFIG_DIR` is pinned to `CLAUDE_HOME` only when the operator explicitly set `CLAUDE_HOME` — left unset (the default), the CLI's own default config dir already matches what `cc-discovery` reads, so the pin is left off rather than pointed at the wrong directory (see `runClaude()`'s comment in `cc-plugin-cli.js` for the incident this fixed). `source` must be `owner/repo`, an `http(s)://` URL, or an absolute path; `spec`/`key` must be `<name>` or `<name>@<marketplace>`; `scope` is `user` (default), `project` or `local`. Validation failures return 400 `EBADARG`; a missing `claude` binary returns 503 `ECLINOTFOUND`; a CLI timeout returns 504 `ETIMEOUT`; a non-zero CLI exit returns **422 `ECLIEXIT`** with the CLI's message plus `stdout`/`stderr`. Successful runs return `{ ok: true, stdout, stderr }` and broadcast `cc_config_changed`. `GET /plugins/available` proxies `claude plugin list --available --json` as `{ installed, available }`.
@@ -1637,6 +1640,7 @@ GET /api/codex-config/config
 GET /api/codex-config/file?path=<absolute-path>
 PUT /api/codex-config/file      Body: { scope, type, name?, content }
 DELETE /api/codex-config/file   Body: { scope, type, name? }
+POST /api/codex-config/project-memory   Body: { dir, content }
 GET /api/codex-config/backups[?scope=&type=]
 GET /api/codex-config/mcp
 GET /api/codex-config/plugins