chore(release): v0.7.1 — lattice 0.7.0 dependency adoption

[ohdearquant]

Release 0.7.1: adopt the published lattice 0.7.0 crates.

Changes

• Workspace version 0.7.0 → 0.7.1; lattice-embed and lattice-fann
  requirements bumped to 0.7.0 (published on crates.io; verified on the
  index per crate against the 0.6.1 pre-state). Lockfiles regenerated,
  including the excluded khive-merge workspace.
• MSRV comment updated: lattice 0.7 requires Rust 1.93, which was already
  the workspace floor.
• MAX_TEXT_CHARS → MAX_TEXT_BYTES across 10 files, following the
  lattice-embed 0.7.0 deprecation (same 32768 value; the constant counts
  UTF-8 bytes, which is what the byte-based production guard always
  enforced — behaviorally identical admission set).
• Removed a stray crates/target symlink that had been committed (a
  target/ gitignore pattern matches directories only, not symlinks).

Compatibility gate (run before the lattice release was published)

Against the lattice 0.7.0 release candidate, with the patch resolution
hard-asserted via cargo metadata (a [patch.crates-io] entry whose
version does not satisfy the requirement is silently ignored — the gate
aborts rather than green-lighting a registry build):

• Full workspace check + clippy clean.
• The lattice 0.7.0 chars→bytes text-limit change is invisible through
  khive: the sole production ingress guard was already byte-based, and
  chars ≤ bytes in UTF-8 means an identical admission set.

Verification on this branch

• make ci green end to end (no-stub guards, lockfile freshness,
  forward-deployed crate checks, fmt, lints, full test suite, release
  build, contract tests: 127 passed).
• ADR-135 F4 hold-time release gate passed with ~10x margin:
  comm.send median 776µs / p95 993µs (bounds 8.5ms / 11ms),
  comm.reply median 891µs / p95 1.15ms (bounds 9.5ms / 12.5ms).

[ohdearquant]

Superseded: the lattice dependency adoption and constant rename landed on main via #1661 against lattice 0.7.1 (this branch pinned 0.7.0), and the remaining workspace version bump belongs in a fresh release cut at release time. Closing rather than rebasing a stale release branch.