fix(to-tickets): remove stray </content> tag from skill and docs

The final line of to-tickets/SKILL.md carried a stray `</content>`
closing tag with no matching opening tag — a packaging/serialization
artifact from the planning-skills refactor (386d4ff), not valid skill
content. The same stray tag had leaked into the generated landing
docs for to-tickets and to-spec. Strip it from all three.

Fixes #495

Co-Authored-By: Claude Opus 4.8 (1M context) <noreply@anthropic.com>

docs/engineering/to-spec.md

@@ -57,4 +57,3 @@ grill-with-docs → to-spec → to-tickets → implement → code-review
 ```
 
 Reach for it after the plan and domain language are resolved, and before you break the work into implementation tickets. Its key neighbours are [grill-with-docs](https://aihero.dev/skills-grill-with-docs), which sharpens the context so the spec is precise, and [to-tickets](https://aihero.dev/skills-to-tickets), which turns the spec into a set of tickets for [implement](https://aihero.dev/skills-implement) to build. When you're unsure which skill or flow fits, [ask-matt](https://aihero.dev/skills-ask-matt) routes you.
-</content>

docs/engineering/to-tickets.md

@@ -54,4 +54,3 @@ grill-with-docs → to-spec → to-tickets → implement → code-review
 ```
 
 It sits between [to-spec](https://aihero.dev/skills-to-spec), which hands it a settled spec with user stories to slice against, and [implement](https://aihero.dev/skills-implement), which builds each ticket, driving [tdd](https://aihero.dev/skills-tdd) internally to write the tests test-first, before its [code-review](https://aihero.dev/skills-code-review) pass. Work the frontier one ticket per fresh context, clearing between them. When you're unsure which skill or flow fits, [ask-matt](https://aihero.dev/skills-ask-matt) routes you.
-</content>