fix(coding-agents): check knowledge pages before reflecting (#3702)

* fix(coding-agents): check knowledge pages before reflecting

* docs(coding-agents): align pages-first guidance

* docs(coding-agents): regenerate the docs-skill reference from the README

The README edit reached skill/SKILL.md and the docs page but not
skills/hindsight-docs/references/sdks/integrations/coding-agents.md, which
is generated from the README too (by scripts/generate-docs-skill.sh). It
still described autoReflect=false as "the tool guide instead tells the
agent to call hindsight_reflect", contradicting the behaviour this branch
introduces, and verify-generated-files failed on the drift.

All four surfaces now carry the same wording.

Claude-Session: https://claude.ai/code/session_01HVZ94d143NPSsZjbnvwqba

* refactor(coding-agents): name the new-goal trigger for what it now does

Code-review follow-ups, no behaviour change:

- REFLECT_ON_GOALS -> PAGES_FIRST_ON_GOALS. The constant is file-local and
  its old name described the pre-change behaviour (reflect first), which is
  exactly the guidance this branch reverses.
- ToolGuideOpts.reflectOnNewGoals kept its name (two call sites depend on
  it) but its doc comment now records what changed and why, per the
  keep-comments-current rule.
- Explain why the negative assertion deliberately omits the `s` flag: it
  guards the old single-line wording, and with `s` it would span newlines
  and match the legitimate hindsight_reflect / FIRST STOP lines below.

Claude-Session: https://claude.ai/code/session_01HVZ94d143NPSsZjbnvwqba

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Co-authored-by: Nicolò Boschi <boschi1997@gmail.com>