Pre-publish docs sweep: README, AGENTS.md, licenses, inline doc fixes

- Add README.md reflecting the v0.1.0 state: 19 AlkType kinds, two
  layout modes, builder + AlkTypeEngine usage example (verified to
  compile and run), validation entry points, crate independence,
  untrusted-schemas guarantee, docs pointers. Mirrors the alkvault
  README structure.
- Add AGENTS.md with alktype-specific git workflow, project
  conventions (no comments, AlkTypeError, untrusted schemas, overflow
  safety, no async, no feature flags, wasm-clean, preserve_order
  load-bearing, no unsafe), verification commands, and ADR/OQ index.
  Blocks auto-commit on semver-relevant public API changes per the
  crates.io 0.1.0 contract.
- Add LICENSE-MIT and LICENSE-APACHE (dual MIT/Apache-2.0, matching
  alkvault and the Cargo.toml license field).
- Cargo.toml: add readme, keywords, categories, rust-version = "1.85".
- Fix broken intra-doc link in builder.rs: DiscriminatorKind ->
  crate::schema::DiscriminatorKind (cargo doc now warning-free).
- N1 (review #002): document is_rfc3339_timestamp as non-strict in the
  function doc comment. Lists the specific gaps (day-of-month per
  month, seconds range, leap seconds) and points consumers needing
  strict validation to chrono/time.
- N2 (review #002): document the FieldValue::Bytes-for-Record API
  asymmetry in the FieldValue enum doc and on read_record_value.
- .opencode/agents/implementation-specialist.md: point to AGENTS.md
  for full convention details (matches the alkvault pattern).
- review #002: mark N1/N2 resolved; all 7 findings now closed.

Verification:
- cargo test --release: 396 tests pass (310 crate + 86 integration)
- cargo clippy --all-targets -- -D warnings: clean
- cargo doc --no-deps: clean (no broken intra-doc link warnings)
- cargo build --target wasm32-unknown-unknown --release: clean
- cargo publish --dry-run --allow-dirty: clean

src/builder.rs

@@ -431,7 +431,8 @@ impl Schema {
 }
 
 /// TUnion discriminator, builder-friendly form. Mirrors
-/// [`DiscriminatorKind`] but constructed via the builder API.
+/// [`crate::schema::DiscriminatorKind`] but constructed via the builder
+/// API.
 #[derive(Debug, Clone)]
 pub enum Discriminator {
     /// Byte-offset discriminator. `offset` is the byte position; `disc_type`