feat(core): render CodeMode catalog deltas from structured snapshots - #38183

Follow-up to #38003, part of the CodeMode catalog work (#36196).

What changed

Moves Code Mode catalog prompting out of @opencode-ai/codemode so core owns all model-facing instruction text, and upgrades the core/codemode instruction source from whole-string replacement to skill-style semantic deltas.

codemode package

• Removed Runtime.instructions(), DiscoveryOptions, and all catalog prose/budgeting; prepare now returns only structured { catalog, searchIndex }
• Newly exported CodeMode.searchSignature and CodeMode.toolExpression(path) so hosts can render exact callable forms — signature construction stays codemode-owned
• Search built-in unchanged

core

• New CodeModeCatalog module (src/codemode/catalog.ts): owns the ported round-robin token budgeting (default 2000), full instruction rendering, and update() semantic diffing via Instructions.diffByKey
• CodeMode.materialize returns a structured catalog instead of a rendered string; ExecuteTool.instructions becomes ExecuteTool.catalog
• CodeModeInstructions stores the sorted structured snapshot with a typed codec, so mid-conversation changes render as tool-level deltas:
  • additions render as new signature lines, removals as exact callable expressions (tools.ns["dashed-name"]), changed signatures as superseding lines
  • full restatement only when the diff is empty, the rendering crosses full/compact modes, or the delta is larger than the full catalog
• Registration order no longer churns durable instruction history (canonical sorted snapshot)
• Fixed a semantic merge conflict on v2: feat(core): deliver CodeMode catalog through instructions #38003 landed importing ./effect/app-node after upstream moved it to @opencode-ai/util/effect/app-node, breaking core typecheck

Notes

• This deliberately overrides spec Q13 (codemode owning catalog rendering) per direction: codemode supplies structured descriptors, opencode owns prompting
• Codemode instruction-prose tests were ported to packages/core/test/codemode/catalog.test.ts, not dropped

Testing

• packages/core: typecheck clean, 1417 pass (1 pre-existing environmental failure in plugin.test.ts)
• packages/codemode: typecheck clean, 1022 pass