chore: release v0.11.6

[vyncint]

What & why

Release v0.11.6, following docs/RELEASING.md steps 1, 2 and 2b:

• version 0.11.6 in [workspace.package] and in the CLI's termlens
  dependency, with Cargo.lock refreshed;
• report@v0.11.6 in the three pinned files (check-report-pin.sh
  passes);
• SKILL.md "Written against termlens 0.11.6", and the bug report form's
  placeholder;
• the CHANGELOG [Unreleased] section moved to [0.11.6] - 2026-10-14,
  with its link definitions. extract-changelog.sh 0.11.6 prints the three
  Fixed bullets the GitHub Release will carry;
• tests/compat/0.11.6/, written by the write_corpus test from this tree.
  It is 0.11.5's twelve files byte for byte, so the rendering did not change.

What the release ships, all merged and reviewed:

• fix: report an exec failure as a spawn error, not a SIGABRT child #566: a program that exists but cannot be executed is a spawn error that
  names the culprit (closes An exec failure after the fork is a runtime abort, not a spawn error (a missing #! interpreter shows killed by signal: Aborted) #563). The responder thread's master duplicate
  is close-on-exec. XTGETTCAP TN reports the last TERM set.
• chore(deps): bump the cargo-minor-patch group across 1 directory with 3 updates #571: libc 0.2.190, insta 1.49.0 and serde_json 1.0.154 in the lockfile
  the CLI installs with --locked.
• ci: repin dtolnay/rust-toolchain to where v1 points now #567, chore(deps): bump the actions-minor-patch group across 1 directory with 2 updates #568, chore(deps): bump dtolnay/rust-toolchain from 7e38f4b43b4db5c8dd498af069a4f6196df1d067 to e2a55d2ffb04f378e9626c28d38b36d230d1e12f #569: CI pins. One effect: the semver job now installs
  cargo-semver-checks 0.51.0, and its selftest still finds both documented
  holes.

The semver baseline (ci.yml, CONTRIBUTING §1) moves to 0.11.6 after
publish, in its own PR, as RELEASING step 5 says.

Verification

• Behaviour diff, published 0.11.5 against this tree: 969 cases, covering
  render in five formats over 104 saved screens, diff pairs, the CLI
  surface, and 35 inspect programs. Two differ, the missing-interpreter and
  CRLF cases, both intended.
• .github/scripts/check-cli-contract.sh passes against the candidate
  binary.
• Stress on fix: report an exec failure as a spawn error, not a SIGABRT child #566's head (b6c101a): 15/15. Stress runs again on the merged
  commit before the tag.

Checklist

• Linked an issue (or explained above why none exists)
• Tests added/updated for the change
• cargo fmt --all and cargo clippy --workspace --all-targets --all-features are clean
• All commits are signed off (git commit -s) — see CONTRIBUTING.md §5
• No AI attribution trailers (no AI co-authors, "Generated with" footers, or bot identities) — see CONTRIBUTING.md §6
• CHANGELOG.md updated under [Unreleased] (user-facing changes only)
• Snapshot changes (if any) were reviewed with cargo insta review, not blind-accepted