feat: add USER.md and TOOLS.md to bootstrap framework

Introduce user profile (USER.md) and machine tool reference (TOOLS.md)
as first-class framework files. Both ship as generic defaults and are
personalized via mosaic init.

- Add USER.md/TOOLS.md defaults and parameterized templates
- Update AGENTS.md load order (6 → 8 steps)
- Update SOUL.md: default name "Assistant", add trash/mental-notes guardrails
- Update install.sh: preserve USER.md/TOOLS.md on reinstall
- Update mosaic-init: interactive USER.md + TOOLS.md generation
- Update mosaic-doctor: existence checks for new files
- Update mosaic launcher: inject USER.md/TOOLS.md into runtime prompt
- Update README: architecture diagram, generic-repo policy note

Co-Authored-By: Claude Opus 4.6 <noreply@anthropic.com>

AGENTS.md

@@ -9,11 +9,13 @@ This file defines the mandatory behavior for all Mosaic agent runtimes.
 Before responding to any user message, you MUST read these files in order:
 
 1. `~/.config/mosaic/SOUL.md`
-2. `~/.config/mosaic/STANDARDS.md`
-3. `~/.config/mosaic/AGENTS.md`
-4. `~/.config/mosaic/guides/E2E-DELIVERY.md`
-5. Project-local `AGENTS.md` (if present)
-6. Runtime-specific reference:
+2. `~/.config/mosaic/USER.md`
+3. `~/.config/mosaic/STANDARDS.md`
+4. `~/.config/mosaic/AGENTS.md`
+5. `~/.config/mosaic/TOOLS.md`
+6. `~/.config/mosaic/guides/E2E-DELIVERY.md`
+7. Project-local `AGENTS.md` (if present)
+8. Runtime-specific reference:
    - Claude: `~/.config/mosaic/runtime/claude/RUNTIME.md`
    - Codex: `~/.config/mosaic/runtime/codex/RUNTIME.md`
    - OpenCode: `~/.config/mosaic/runtime/opencode/RUNTIME.md`