refactor(claude-md): split shared base into module fragments, inject name at runtime

Move every agent-specific instruction out of the shared container/CLAUDE.md
so the base is genuinely universal. Persona/identity now comes from the
system-prompt addendum (buildSystemPromptAddendum now takes assistantName
and prepends "# You are {name}"). Per-module instructions live alongside
each MCP tool source:

  container/agent-runner/src/mcp-tools/core.instructions.md
  container/agent-runner/src/mcp-tools/scheduling.instructions.md
  container/agent-runner/src/mcp-tools/self-mod.instructions.md

composeGroupClaudeMd() scans that directory and emits `module-<name>.md`
fragments as symlinks to /app/src/mcp-tools/<name>.instructions.md (valid
via the existing RO source mount). Skill fragments renamed to
`skill-<name>.md` for naming consistency with `module-*` and `mcp-*`.

Mount tightening so composer-managed files can't be clobbered by agent
writes: nested RO mounts for /workspace/agent/CLAUDE.md and
/workspace/agent/.claude-fragments/. CLAUDE.local.md (per-group memory)
stays RW as the only writable CLAUDE.md-family file.

.gitignore: ignore CLAUDE.local.md, .claude-shared.md, .claude-fragments/
everywhere, and simplify groups/ rules to ignore the whole tree (per-
installation state, not tracked).

Co-Authored-By: Claude Opus 4.7 (1M context) <noreply@anthropic.com>

container/agent-runner/src/index.ts

@@ -45,12 +45,13 @@ async function main(): Promise<void> {
 
   log(`Starting v2 agent-runner (provider: ${providerName})`);
 
-  // Destinations addendum is the only runtime-generated context we inject.
-  // Agent instructions are loaded by Claude Code from /workspace/agent/CLAUDE.md
-  // (host-composed at spawn, imports /app/CLAUDE.md and fragments) plus
-  // /workspace/agent/CLAUDE.local.md (agent memory) — no need to read them
-  // manually.
-  const instructions = buildSystemPromptAddendum();
+  // Runtime-generated system-prompt addendum: agent identity (name) plus
+  // the live destinations map. Everything else (capabilities, per-module
+  // instructions, per-channel formatting) is loaded by Claude Code from
+  // /workspace/agent/CLAUDE.md — the composed entry imports the shared
+  // base (/app/CLAUDE.md) and each enabled module's fragment. Per-group
+  // memory lives in /workspace/agent/CLAUDE.local.md (auto-loaded).
+  const instructions = buildSystemPromptAddendum(config.assistantName || undefined);
 
   // Discover additional directories mounted at /workspace/extra/*
   const additionalDirectories: string[] = [];