fix: reach the phase with the catalog notice

[kyy-logs]

The exploration prompt already promised that "the round's own facts say whether any
history exists, and under which categories". Nothing carried that fact, and the module
could not load at all: experience_catalog.py imported ExperienceCatalogNotice from
core.models, which never defined it.

The pointer now reaches the phase

• list_experiences takes an optional category, and a page lists every card when none is
  given: the three categories say what a card is about, not who may read it. Requiring a
  guess made the category a gate -- a phase that asked about workflow while the library
  held one framework card was told the library was empty.
• each catalog entry names its own category, so a cross-category page is self-describing.
• core.models gains ExperienceCatalogNotice, AgentContext carries it, and the phase
  message renders it. Only the pointer travels -- a count and the categories. Names and
  bodies stay behind list_experiences and read_experience, so browsing remains the
  phase's own decision.

Verified

• Full suite: 882 passed, 10 skipped (out-of-repo basetemp; the 10 are the known
  environment gaps -- no ripgrep, no Windows symlink privilege).
• Unit: the page's own category, and the unfiltered page that lists every card.
• Real model runs on pytest-8906: with a one-card library the phase message carries
  "experience_catalog":{"categories":["framework"],"count":1}; with experience off the
  field is absent. Neither run leaks the card's name or description.

🤖 Generated with Claude Code