feat(uik): introduce User Intent Kit as an IAK feature

[ThinkOffApp]

Rationale

We talked in the room about whether to spin User Intent Kit out as its own repo and decided against it: launching a zero-star repo for a layer that only makes sense alongside IAK's room I/O, session control, confirmation registry, and receipts log would orphan both halves. Instead, IAK ships UIK as a named feature. Architecture stays modular internally (its own package), marketing leads with "IAK now includes UIK."

What landed

• docs/UIK.md - concise design doc covering what UIK is, why it lives in IAK, the seven elements of an Intent (goal, constraints, approval gates, ownership, receipts, escalation, done criteria), a raw-chat vs Intent example, and how it composes with existing MCP tools (room_post, room_recent, room_ack, tmux_run, the confirmation registry).
• packages/uik/ - new @thinkoff/uik TypeScript package. Mirrors packages/core conventions (ESM, tsc build, AGPL-3.0-only, ThinkOff author).
  • src/intent.ts: Intent, Constraint, ApprovalGate, Owner, Receipt, Escalation, DoneCriterion, ValidationResult interfaces plus validateIntent() with required-field and non-empty-handle / non-empty-doneCriteria checks.
  • src/index.ts: re-exports.
  • package.json, tsconfig.json, README.md.
• README.md - one new section ("User Intent Kit") with a ToC entry, linking to docs/UIK.md. No other changes.

Root package.json has no workspaces array and there is no root tsconfig.json, so nothing to wire there. The package builds standalone against its own devDeps (typescript 5.9.3, matching core).

Out of scope

Intentionally not in this PR, to land once the shape settles:

• Concrete reference implementation of approval-gate execution against the existing iak-mcp-daemon confirmation registry.
• New MCP tools intent_create, intent_status, intent_close exposed by bin/iak-mcp.mjs.
• Receipt-log integration that keys entries by Intent id.
• Deeper semantic validation (constraint family schemas, approver existence, gate ordering).

Test plan

• cd packages/uik && npx tsc --noEmit passes (verified locally against typescript 5.9.3, no errors).
• Existing IAK tests still pass (npm test at the root) - UIK doesn't touch any runtime code paths.
• docs/UIK.md and packages/uik/README.md render correctly on GitHub.
• Manually construct the example Intent from the docs and confirm validateIntent() returns { ok: true, errors: [] }; then drop a required field and confirm the matching error fires.

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