feat(agent): interactive TUI launcher + identity + TOOLS.md (#35)

- scripts/agent.sh <name>: launches interactive pi TUI in the container
  with contracts + optional mission + agent identity + named session +
  optional workspace/tools; the Mosaic alternative to vanilla pi
- pi adapter: MOSAIC_INTERACTIVE branch (clean TUI, no -p, no initial
  prompt); headless exec rebuilt via positional args (no word-splitting
  on the request); MOSAIC_AGENT_NAME optional in headless
- loader: AGENT IDENTITY section when the launcher names the agent
- compose: fixed command removed (request defaults live in run-agent.sh);
  MOSAIC_INTERACTIVE/MOSAIC_AGENT_NAME passthrough
- docs/TOOLS.md: full on-demand tool reference; AGENTS.md routes to it
- RELEASE -> 0.0.8 (container change); build verified

Closes #35

missions/hello.json

@@ -1,7 +1,7 @@
 {
   "missionVersion": 1,
   "id": "m-hello",
-  "objective": "Prove the startup marker path of the mosaic-poc-agent.",
+  "objective": "Verify the startup marker path.",
   "directives": [
     "Startup verification requests are answered with the marker only.",
     "No explanation, no formatting."