docs(ts): document the solution-root TypeScript project layout

New authoritative section docs/development.md#typescript-project-layout
(five files, three roles, the program-vs-resolution principle and its two
disciplines), two repo conventions in AGENTS.md, package tsconfig shape in
packages/AGENTS.md, cookbook touch-lists updated for the two aggregates,
test source-plane rule in docs/testing.md. Decision record: new Agent Note
2026-07-22-tsconfig-solution-root-two-aggregates; ts-build-config note
updated in place (tsc-first pipeline unchanged); the two GUI RFCs now name
tsconfig.host.json. All bilingual pairs re-recorded. Doc budget ceilings
raised: AGENTS.md 1680, docs/testing.md 1020, packages/AGENTS.md 660 (two
new one-line conventions and one new section on already-near-ceiling docs).
Mission spec for the code-side migration: missions/tsconfig-single-graph-migration.md.

packages/AGENTS.md

@@ -19,6 +19,7 @@ These package-specific rules supplement the repo-wide [conventions](../AGENTS.md
 
 Naming notes:
 
+- **Package tsconfig shape:** extends `tsconfig.base.json` (client: `tsconfig.base.client.json`), `rootDir: src`, `outDir: lib/types`, a `references` entry per workspace dependency plus `support/invariants`; registered in exactly one aggregate — host packages in `tsconfig.host.json`, client in `tsconfig.client.json` ([layout](../docs/development.md#typescript-project-layout)).
 - `src/types.ts` contains only types — no runtime code.
 - Tests live at package level under `tests/`, not `src/__tests__/`.
 - A package's README and JSDoc are part of the change: altered behavior (config keys, defaults, error codes, wire fields) updates them in the same commit. `doc-sync` gates what it can; apply [dsh-prose-standard](../.agents/skills/dsh-prose-standard/SKILL.md) for complete, concise prose and verify accuracy against code.