feat(plugin): ship the agents from a single root agents/ directory

Move .claude/agents/ and server/data/agent-templates/ship-feature-lane/
into one agents/ at the repo root — which IS the plugin root, so all five
agents now ship with the ccam plugin as ccam:<name>, the same way skills
already do.

The two pipeline agents were byte-identical copies in both places; that
duplication is gone. `ccam lanes agents install` now reads them straight
from agents/, so the per-lane copy in <lane>/.claude/agents/ still gives
the bare `subagent_type: qc-local` the ship-feature-lane skill prefers.
Skill and docs record both names: bare inside a lane, ccam: as fallback.

docs/LANES.md

@@ -1086,7 +1086,7 @@ ccam skills install
 
 Copies `skills/ship-feature-lane/` into `~/.claude/skills/ship-feature-lane/` (overwrites on reinstall — run it again after pulling an update to the skill), which restores the bare `/ship-feature-lane` name. One-time per machine, same as `ccam lanes agents install` is one-time per lane.
 
-**Agents are the deliberate exception.** `qc-local` and `senior-gate-reviewer` are *not* shipped as plugin agents: a plugin agent is addressed as `ccam:qc-local`, and the skill dispatches them by the bare `subagent_type: qc-local`. `ccam lanes agents install` writes them into the lane's own `.claude/agents/`, which is also the highest-priority agent source — so the lane's copy wins over anything global.
+**Agents come from the same plugin, under two names.** `qc-local` and `senior-gate-reviewer` live in `agents/` at the repo root, so the plugin exposes them as `ccam:qc-local` / `ccam:senior-gate-reviewer`. `ccam lanes agents install` copies those same files into the lane's own `.claude/agents/` — the highest-priority agent source — which is what makes the bare `subagent_type: qc-local` the skill prefers resolve inside the lane. Either name reaches the same definition; the skill falls back to the `ccam:` form when the lane copy is missing.
 
 ### Invoking the skill
 
@@ -1155,13 +1155,13 @@ GENERATED_MERGE_PATHS="api/openapi.json api/client.ts"
 
 ### Installing the QC/gate agents: agents install
 
-Stage 6 (browser QC) and Stage 7 (senior GO/NO-GO gate) run as subagents — `qc-local` and `senior-gate-reviewer` — that must exist in the lane's own `.claude/agents/` before the skill can launch them:
+Stage 6 (browser QC) and Stage 7 (senior GO/NO-GO gate) run as subagents — `qc-local` and `senior-gate-reviewer`. The plugin already ships them as `ccam:qc-local` / `ccam:senior-gate-reviewer`; installing them into the lane's own `.claude/agents/` is what makes the bare names work there:
 
 ```bash
 ccam lanes agents install
 ```
 
-Writes both agent templates into `<lane>/.claude/agents/` and adds that directory to the lane's local `.git/info/exclude` (never the tracked `.gitignore` — this is a per-clone runtime concern, not an app-repo change). Idempotent and never automatic, the same shape as `ccam lanes proof-link` — a session installs the agents explicitly, once, before a lane's first run through Stage 6/7 (or after a CCAM upgrade ships updated templates — reinstalling overwrites, it doesn't merge).
+Writes both agent definitions (from the repo's own `agents/`, the same files the plugin ships) into `<lane>/.claude/agents/` and adds that directory to the lane's local `.git/info/exclude` (never the tracked `.gitignore` — this is a per-clone runtime concern, not an app-repo change). Idempotent and never automatic, the same shape as `ccam lanes proof-link` — a session installs the agents explicitly, once, before a lane's first run through Stage 6/7 (or after a CCAM upgrade ships updated templates — reinstalling overwrites, it doesn't merge).
 
 **Credentials are not embedded.** Unlike Shipyard's original per-lane agent generation, these templates carry no QA account credentials — this repo has no seeded-QA-account system yet. `qc-local` degrades gracefully: if it hits a login page with no credentials block present, it reports `LOCAL-QC: FAIL — login required, no seed-account mechanism configured for this profile` rather than guessing.