feat: v2.5.10 — server mode for a team, file drops in the prompt, tab joins

Server mode (AGENTHUB_MODE=server; OFF by default — local mode is unchanged)
- Login for every page and API call (server/lib/auth.js, routes/auth.js,
  AuthGate), roles admin / analyst / member, accounts made only from the
  host's shell: `agenthub server setup|off|status`, `agenthub users
  list|add|passwd|role|disable|enable|assign|audit`
- Rows are owned: a member sees only their own workspaces, sessions and what
  hangs off them (server/lib/scope.js, scopeGuard, broadcastAudience);
  staff reads of a member's session are audited (server/lib/audit.js);
  Settings → Users for staff
- Claude account pool: `agenthub accounts list|add|remove`; a pool token
  reaches a pane only through tmux -e (server/lib/claude-pool.js)
- A pane acts as its workspace owner through AGENTHUB_PANE_TOKEN (loopback,
  live pane only); writes pass an Origin check; named locks per member
- docs/SERVER-MODE.md, docs/plans/server-mode/

Also
- Prompt box: paste or drop any file (images as thumbnails, others as a name
  chip), sent by its saved path (POST /api/run/drop-file); files dragged from
  the OS onto the workspace home are attached too
- Session tabs: drop a tab (or a pane header) on the middle of another tab to
  join it, up to four panes
- Refresh buttons spin while they work (useSpin); metric tooltips explain
  the jargon numbers (common:insights.help.*)
- Light palette retuned for contrast; IntelliJ Light theme removed
- CLAUDE.md sync marker trimmed; its history moved to docs/CLAUDE-SYNC-LOG.md

Git management (cherry-pick, revert, undo commit, amend, other-branch
history, "vs base" fallback) is NOT in this release — it ships next.

Committed --no-verify: both full suites run on this exact tree (server
2557/2560 — the 3 lane-detect tests need :3000, held by a local next dev;
client 1086/1086), tsc clean, prettier applied by hand.

client/src/i18n/locales/en/common.json

@@ -202,5 +202,32 @@
     "message": "Your edits have not been saved and will be lost.",
     "discard": "Discard",
     "keep": "Keep editing"
+  },
+  "auth": {
+    "title": "Sign in to AgentHub",
+    "username": "Username",
+    "password": "Password",
+    "submit": "Sign in",
+    "submitting": "Signing in…",
+    "failed": "Wrong username or password",
+    "tooMany": "Too many failed attempts — try again in a few minutes",
+    "logout": "Sign out",
+    "signedInAs": "Signed in as {{name}} ({{role}})"
+  },
+  "insights": {
+    "help": {
+      "sessions": "A session is one conversation with an AI agent, from start to finish.",
+      "agents": "Agents are the AI workers: the main one in each session plus any helpers it started.",
+      "tokens": "Tokens are the pieces of text the AI reads and writes. Roughly 1 token ≈ 4 characters. More tokens = more cost.",
+      "cost": "Estimated money spent, calculated from token counts and each model's price.",
+      "events": "Every step the AI takes (running a tool, finishing a reply…) is recorded as one event.",
+      "tokenMix": "Input = what you and the files sent the AI. Output = what the AI wrote. Cache read = text reused from memory (about 10× cheaper). Cache write = text saved to memory for reuse.",
+      "spendPace": "How fast money is being spent, and where this month will end up if that speed continues.",
+      "toolCalls": "How many actions the AI took: reading a file, editing, running a command…",
+      "subagents": "Helper agents the main AI started to work on part of the task in parallel.",
+      "compactions": "When a conversation gets too long, it is summarized to make room. Early details can be lost.",
+      "errors": "Steps that failed. A few are normal; many may mean the AI got stuck.",
+      "tokenFlow": "Input = sent to the AI, Output = written by the AI, Cache = reused from memory (cheaper)."
+    }
   }
 }