refactor(kb): one definition per fact, one setting per style (v0.13.1)

[cskwork]

v0.13.1 — kb.sh without the duplication v0.13.0 shipped with

A refactor of tools/kb.sh with one intentional behaviour change. Output of
show, index, list, search and harvest is unchanged byte for byte
except where noted; the gates are untouched.

Changes

• One definition of "unmerged harvest". index and harvest each had their
  own loop deciding which open features still hold candidates; both now read
  kb_unmerged. index's two passes over the features (overview table, then
  one section each) share kb_meta for state, date, tags and title instead of
  extracting them twice.
• kb_get replaces the nine kb_real "$(kb_field …)" idioms; kb_closed
  replaces the three awk one-liners over CLOSED.
• Dropped: the ## Summary-inside-intent.md fallback. It supported a format
  no store ever wrote — designed and abandoned inside the v0.13.0 work — and its
  helper kb_summary_where with it. summary.md is the digest.
• Dropped: index --obsidian. The page style is a property of the store, and
  init.sh and close.sh regenerate the page without flags, so
  index_style: obsidian in the store's config.md was already the setting
  that mattered. One setting, one place; the flag is now an unknown option.
• Fixed on the way: show printed Tags: only when the intent carried them,
  although the tags live in summary.md — the meta line now uses the same
  kb_tags the page uses. A feature that carries a CLOSED record but was never
  archived (an interrupted close) is now treated as closed everywhere on the
  page — sorted by closed_at and labelled closed <date> — where before only
  archive/ entries were.
• Internal record lines use \037 as separator, not a tab: a tab is IFS
  whitespace, so read collapses adjacent tabs and an empty field (no tags, no
  date) shifted the fields after it.
• Header comment shortened; tools/kb.sh 605 → 538 lines.

Checked against a real store (84 open, 2 archived, Korean records): the page
and the show digests are byte-identical to v0.13.0 except for the two lines
the fixes above describe; harvest output is identical.

Validation

• bash gates/knowledge-test.sh → KNOWLEDGE-TEST PASS, 144 assertions
  (section H rewritten for the config-only style; the flag refusal is asserted)
• bash gates/selftest.sh → SELFTEST PASS
• bash gates/e2e.sh → E2E PASS, 152 · bash gates/autotest.sh → AUTOTEST PASS, 195