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/echo-agent/src/echo-tool.ts

@@ -1,19 +1,19 @@
 import type { Context } from 'cordis'
+import { defineTool } from '@deepseek-ai/dsh-tools'
 
 export const name = 'echo-tool'
 export const inject = ['tools']
 
 export function apply(ctx: Context) {
-  ctx.tools.register({
+  ctx.tools.register(defineTool({
     name: 'echo',
     description: 'Echo the given text back, uppercased.',
     parameters: {
-      type: 'object',
-      properties: { text: { type: 'string' } },
-      required: ['text'],
+      text: { type: 'string', required: true },
     },
-    async execute(args: any) {
-      return [{ type: 'text', text: `ECHO: ${String(args?.text ?? '').toUpperCase()}` }]
+    async execute(args) {
+      // args is typed: { text: string }
+      return [{ type: 'text', text: `ECHO: ${args.text.toUpperCase()}` }]
     },
-  })
+  }))
 }