fix(typedef): fix code examples and cross-doc inconsistencies from second review

- Fix code examples hardcoding little-endian: read_string, write_string,
  read_string_indirect now take endian parameter and use match on Endian.
- Fix TUnion dispatch examples: remove undefined functions (read_u8,
  read_field, read_struct, read_f32_raw), remove Value returns
  (contradicts 'no intermediate Value tree'), add endian-aware
  discriminator reading for Uint8/Uint16/Uint32.
- Fix read_f32 example: inline the endian-aware conversion instead of
  calling undefined read_f32_raw; document it as aligned-mode only.
- Fix architecture README: 16→17 kinds in schema-layer and validation
  descriptions.
- Fix ADR-095: clarify validation operates on Value instances, not raw
  byte buffers directly. Fix 'defense in depth' paragraph.
- Fix ADR-097: add §3a defining TRecord 'values' property shape.
- Fix ADR-098: TTimestamp format ISO 8601→RFC 3339.
- Tighten OQ-071 impacts field: state what IS blocked, not just what
  isn't.

docs/architecture/questions/071-builder-api-for-schema-construction.md

@@ -8,10 +8,12 @@
 - **Door type**: Two-way (additive — a builder API can be added without
   changing the existing JSON-consumption path)
 - **Priority**: medium
-- **Impacts**: No current consumer. Schemas are authored in TypeBox (JS)
-  or hand-written JSON for v1. A Rust builder API would enable
-  programmatic schema construction in Rust without depending on a JS
-  toolchain, but no current consumer needs this.
+- **Impacts**: Blocks programmatic schema construction in Rust without a
+  JS toolchain. Any consumer that wants to build typedef schemas at
+  runtime from Rust code (rather than loading pre-authored JSON) must
+  construct the JSON manually or depend on TypeBox. Does NOT block any
+  current consumer — all v1 consumers (SFTP, metatensor, binary call
+  frames, TTY negotiation) use pre-authored schemas.
 - **Blocked on**: A concrete need for programmatic schema construction
   in Rust. The current consumers (SFTP, metatensor, binary call frames,
   TTY negotiation) all have schemas that can be hand-written or generated