Bump TypeScript to 6.x once madge accepts it

[chrisreddington]

Context

Dependabot PR #188 proposed bumping typescript from ^5.9.3 to ^6.0.3 as part of the npm-development group. Install fails with ERESOLVE because:

• madge@8.0.0 declares peerOptional typescript@"^5.4.4", which excludes TS 6.x.
• madge@latest is still 8.0.0 — no released version accepts TS 6 yet.
• typescript-eslint@8.59.4 already accepts >=4.8.4 <6.1.0, so it is not a blocker for TS 6.0.x.

Runtime compatibility looks fine: madge → dependency-tree → detective-typescript@14.1.2 already declares typescript: "^5.4.4 || ^6.0.2" in its own peer range. The blocker is purely install-time peer metadata that hasn't been updated upstream.

Upstream tracking

• Issue: pahen/madge#462 — typescript `6.0.3`? (open, no maintainer response)
• PR: pahen/madge#460 — chore(package): typescript 6 as peer optional (open, mergeable, not yet merged, no new release cut)

What was done in PR #188

• Reverted only the typescript bump (kept the other seven dev-group bumps).
• Added a Dependabot ignore rule in .github/dependabot.yml blocking future major-version proposals for typescript until this issue is closed. (Dependabot will still propose TS 5.x patch/minor bumps.)

Exit checklist (when madge ships a release that accepts TS 6)

1. Remove the typescript version-update:semver-major entry from .github/dependabot.yml.
2. Let Dependabot re-propose the TS 6 bump in the next scheduled run (or manually trigger one).
3. Verify on that PR: npm ci, npm run verify, and npm run debt:circular all clean.
4. Close this issue, referencing the merged Dependabot PR.

[chrisreddington]

Upstream tracking links for quick reference:

• madge issue: typescript 6.0.3? pahen/madge#462 (typescript 6.0.3?) — open, no maintainer response yet.
• madge PR: chore(package): typescript 6 as peer optional pahen/madge#460 (chore(package): typescript 6 as peer optional) — open, mergeable, not yet merged. This is the one to watch — once it merges and madge cuts a release, this issue's exit checklist becomes actionable.