Document the codebase thoroughly and tighten type safety

Docs: per-folder README.md for packages/ (family overview + one per
package: service, events, API, extension points, TODOs), examples/,
and examples/echo-agent/; folder-level AGENTS.md (+ CLAUDE.md
symlinks) for packages/ and vendor/; module-level doc comments in
every packages/*/src file; richer JSDoc on all exported API
(event side effects, disposal contracts, error behavior). Root
AGENTS.md gains a "Type Safety and Documentation" policy section:
the codebase aims to be very type-safe and well documented; type
gymnastics are acceptable in core packages when they improve
plugin-author DX; verbose docs are fine as long as they stay strictly
in sync with the code.

Type safety: removed the upstream-inherited "noImplicitAny": false
from tsconfig.base.json — packages/* now compile under full strict
mode; vendor/loader and vendor/include set it locally (vendor/cordis
already did). Eliminated every `: any` / `as any` from packages and
examples (catch clauses use unknown + a CodedError narrowing type;
event data access uses discriminated-union narrowing).

Typed tool schemas: new @deepseek-ai/dsh-tools schema DSL —
SchemaSpec with per-property `required: true` booleans, type-level
InferArgs<S>, a runtime SchemaSpec → JSON Schema converter, and
defineTool() so first-party tools get typed execute(args) with zero
casts (raw JSON Schema still accepted for MCP interop; chosen over
schemastery because it targets JSON Schema generation directly).
echo-tool and all test tools migrated; +7 tests.

examples/README.md

@@ -0,0 +1,17 @@
+# Examples
+
+Runnable demos (not workspaces) that showcase how the harness is wired.
+
+## echo-agent
+
+A mock model + echo tool + stdio UI + JSONL persistence demo. Demonstrates:
+
+- Loading plugins from a `cordis.yml` via `@cordisjs/plugin-loader` + `@cordisjs/plugin-include`
+- Registering a mock `LlmAdapter` (streaming scripted responses)
+- Registering a tool via `ctx.tools.register()`
+- Persisting session events to JSONL via the `session/event` + `session/flush` pattern
+- A minimal stdio UI consuming `agent/stream-chunk` and session events
+
+Run with: `yarn demo` (or `node --expose-internals --import tsx examples/echo-agent/start.ts`)
+
+When prompted, type "echo <something>" to trigger a tool call round-trip.