fix(seer): include selected projects in page LLM context (#123036)

Closes AIML-3422.

Structured LLM page context on Issues/Explore was under-scoping the
agent: Explore spans/logs/metrics/etc. omitted page-filter projects
entirely, and Issues only sent slugs from currently visible rows. ASCII
footnotes only had slugs (no ids).

Adds a shared `getSelectedProjectsForLLMContext` / hook that emits
`projectIds`, `projectSlugs`, and `isAllProjects`, wires it through
Issues, Explore (spans/logs/metrics/profiling/releases/replays), and
Dashboards, and includes `slug (id: …)` in ASCII project footnotes.

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Requested by **Dhrumil**.
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Co-authored-by: sentry-junior[bot] <264270552+sentry-junior[bot]@users.noreply.github.com>
Co-authored-by: Dhrumil Parekh <dhrumil.parekh@sentry.io>
Co-authored-by: Dhrumil <109983869+Dhrumil-Sentry@users.noreply.github.com>