[WIP] Add Galaxy view to the Content Graph

[epeicher]

What

A second render mode for the Content Graph window, toggled with a Graph / Galaxy segmented control in the toolbar. Galaxy renders the corpus as a starfield: every post is a tiny additive-blended dot, each group-by cluster glows as a coloured nebula with a name + post-count label at its heart, and recently-edited or focused posts twinkle.

Visual encoding

Channel	Meaning
Colour	Active group facet (hashed hue per term/author, chronological ramp for year / year-month)
Brightness	Comments + word count, log-normalised
Twinkle	Modified in the last 30 days, or the focused post + neighbours

Galaxy chrome

• All / Drafts / Recent tabs (drafts = your own drafts, now included in the payload; recent = modified in the last 30 days)
• Min comments + Zoom sliders, "X of Y visible" readout
• Bottom legend, hover tooltips, click-to-focus opens the same detail panel as Graph view
• Last-used view persists per user (desktop_mode_content_graph_view user meta, saved over REST)

Server changes

• Per-node payload gains comment_count, word_count (shortcode/tag-stripped), modified_ts
• The posts query now includes the current user's own drafts; the transient cache key is bucketed per user so one user's drafts never surface in another's payload
• Cache prefix bumped cg2_ → cg3_ (schema change, one-time rebuild)

Layout notes (tuned against a 1,000-post seeded corpus)

• Single-membership commit: each dot clusters under its first group key only. With realistic 2-3-terms-per-post data, multi-membership pulls chain every cluster together and the layout collapses into one ball. Colour, forces, nebulae, and labels all share the commit.
• Hyperlink springs drop to near zero while grouping is active (one cross-cluster link otherwise out-pulls the attractor).
• Labels sit at the cluster centroid and fade in together with the nebulae only after clusters visibly separate, so convergence doesn't render as a stack of names over one blob.
• Cluster radius = 80th-percentile member distance (a stray dot can't balloon a nebula).
• Auto-fit-follow keeps the camera framing the layout while the sim spreads it; any manual wheel/drag cancels it. The resize observer resizes the Pixi renderer explicitly (Pixi's resizeTo ignores element resizes, which left the canvas stale after window maximize).
• Dot taps vs background clicks reuse GraphScene's nodeClickActive pattern so selecting a dot doesn't immediately close its own panel.

Testing

• npm run lint, npm run typecheck clean; npm run test:js 1,577 tests green (new: content-graph-galaxy.test.ts covering the brightness curve + tab filter predicate)
• New PHPUnit coverage for the payload fields (test_galaxy_payload_fields_populated)
• Browser-verified end to end on a 1,001-post / 25-category / 36-tag corpus: grouping by category, tag, and year-month; maximize/restore; view-toggle round trips; selection + deselection; view persistence across reopen

Notes for review

• galaxy-scene.ts is a sibling of scene.ts, not an extension — the two share the ForceSim and the payload types but nothing at the render layer, so keeping them separate avoids "is the mode active" branching through the existing scene.
• Docs: Content Graph has no public-contract docs surface (internal feature window), so no doc updates ship with this.