docs(examples): coder-loop + researcher-loop + mcp-delegation + fleet-delegation

[tangletools]

Summary

Add four runnable examples covering the driven-loop kernel (0.19+), the
canonical profile presets, the MCP delegation server, and fleet vs sibling
placement. Existing examples covered basic primitives but nothing post-0.18.

• coder-loop/ — `coderProfile` + `runLoop` + `FanoutVote`; two
  parallel coder iterations through a synthetic sandbox client; validator
  scores test + typecheck + diff cap; kernel picks the winner.
• researcher-loop/ — same shape via `researcherProfile` from
  `@tangle-network/agent-knowledge/profiles`; second iteration leaks into
  a foreign namespace and the validator hard-fails it.
• mcp-delegation/ — the literal `AgentProfile.mcp` entry a product
  passes to `sandboxClient.create`, plus a stdio JSON-RPC smoke that
  spawns the locally-built `agent-runtime-mcp` bin and asserts the five
  canonical tools surface (`delegate_code`, `delegate_research`,
  `delegate_feedback`, `delegation_status`, `delegation_history`).
• fleet-delegation/ — `TANGLE_FLEET_ID` env flip; runs both
  `createSiblingSandboxExecutor` and `createFleetWorkspaceExecutor`
  against structural stubs; ASCII topology diagram.

`examples/README.md` gains a "Trace derivation" section with the diagram
showing how `loop.iteration.ended` events flow into `RuntimeRunHandle`,
the ingestion ndjson, analyst loops, and the production-loop CI gate.
Top-level README adds the four entries to the example list.

Bumps `DEFAULT_SERVER_VERSION` in `src/mcp/server.ts` to match the
package version so the `initialize` smoke reflects the actual build.

Version bump: 0.21.0 → 0.21.1 (examples + docs + minor server-version sync).

Test plan

• `pnpm typecheck` — clean
• `pnpm test` — 24 files / 235 tests pass (unchanged)
• `pnpm exec biome check src tests examples` — clean
• `pnpm build` — clean
• `pnpm tsx examples/coder-loop/coder-loop.ts` — winner picked, valid=true, score=0.996
• `pnpm tsx examples/researcher-loop/researcher-loop.ts` — winner picked, valid=true, score=0.700
• `pnpm tsx examples/mcp-delegation/mcp-delegation.ts` — server: agent-runtime-mcp@0.21.1; all 5 tools listed
• `pnpm tsx examples/fleet-delegation/fleet-delegation.ts` — three round-robin dispatches across worker-a/b/c