perf: lighter, louder local install — vendored ReDoc, bootstrap failures shown in the session

- Plugin bootstrap: a failed npm install, a Node older than 22.5 or a failed UI
  build is recorded in runtime/last-failure.json; the next SessionStart prints
  it once as a systemMessage naming the log and /agenthub-doctor (a different
  failure is reported again; a successful bootstrap clears it). The foreground
  pass checks the Node version itself and spawns no worker on an old Node.
- ReDoc: the standalone bundle (redoc 2.5.4, MIT, licence files kept) is
  vendored under server/vendor/redoc/ and the `redoc` dependency dropped —
  a runtime install (npm ci --omit=dev --ignore-scripts) goes 126 MB -> 45 MB.
  vendor/ is excluded from the header audit and prettier.
- git missing from PATH: lane git actions answer 503 EGITMISSING with the
  install command instead of a bare ENOENT.
- package.json engines: node >=22.5.0 (node:sqlite), matching MIN_NODE.
- Docs: INSTALL.md is the one install/setup guide (SETUP.md merged in and now a
  pointer); no VS Code extension claim, one client-install hint, no
  windows-build-tools, better-sqlite3 notes scoped to checkouts, new
  "Plugin bootstrap never comes up" troubleshooting entry.

docs/README.md

@@ -9,8 +9,7 @@ Comprehensive documentation for the Agent Dashboard project.
 - [Architecture Overview](../ARCHITECTURE.md) - System design and technical reference
 - [I18N Architecture](./I18N.md) - Internationalization architecture and usage guide
 - [CLI Reference](./CLI.md) - The `agenthub` terminal CLI: every command, discovery, safety model
-- [Setup Guide](../SETUP.md) - Installation and configuration
-- [Installation](../INSTALL.md) - Detailed installation instructions
+- [Installation & setup](../INSTALL.md) - Installation, configuration and troubleshooting
 
 ---
 
@@ -20,7 +19,7 @@ Comprehensive documentation for the Agent Dashboard project.
 
 ```mermaid
 graph TB
-    Start[Start Here] --> Setup[SETUP.md<br/>Installation & Config]
+    Start[Start Here] --> Setup[INSTALL.md<br/>Installation & Config]
     Start --> Architecture[ARCHITECTURE.md<br/>System Design]
     
     Setup --> Client[Client README<br/>React UI docs]
@@ -62,7 +61,7 @@ graph TB
 
 ```mermaid
 graph LR
-    A[New to Project] --> B[Read SETUP.md]
+    A[New to Project] --> B[Read INSTALL.md]
     B --> C[Install Dependencies]
     C --> D[Run npm run dev]
     D --> E[Open localhost:5173]
@@ -75,7 +74,7 @@ graph LR
 
 1. Install the system packages — `node` (20+), `git`, and `tmux` (the run
    console has no fallback without it): [INSTALL.md → Step 0](../INSTALL.md#step-0--system-packages)
-2. Read [SETUP.md](../SETUP.md)
+2. Read the rest of [INSTALL.md](../INSTALL.md)
 3. Run `npm run setup`
 4. Run `npm run dev`
 5. Open browser to `http://localhost:5173`
@@ -287,7 +286,7 @@ graph LR
 **Documentation:**
 - [Hook System Guide](./HOOKS.md)
 - [Hook Processing](../server/README.md#hook-processing)
-- [Installation](../SETUP.md#install-hooks)
+- [Installation](../INSTALL.md#hook-auto-installation)
 
 ---
 
@@ -441,4 +440,4 @@ This documentation covers:
 - ✅ **Internationalization** - Language resources, switching flow, locale formatting, rollout checklist
 - ✅ **Development guides** - Setup, testing, contributing
 
-**Start with:** [SETUP.md](../SETUP.md) for installation, then explore specific areas based on your role.
+**Start with:** [INSTALL.md](../INSTALL.md) for installation, then explore specific areas based on your role.