feat(session): console game library — Skia coverflow + SkSL aurora, --browse (phase 4b)

The run loop grows a browse mode: the console library idles between
streams in ONE window (no gamescope handoff), overlay actions launch
sessions via run_browse's callback, session end returns to the library.
The Overlay contract gains menu routing (MenuEvent → haptic pulse),
action draining, and session-phase edges.

pf-console-ui ports the GTK launcher wholesale: the coverflow's springs,
cursor arithmetic and recede/tilt constants move verbatim with their
tests (plus new projection tests — focused-card centering, the inner-
edge-recedes corridor); paint order is draw order (the gtk::Fixed
restack hack is gone); the aurora renders as an SkSL runtime shader at
full rate on every box (the 30 Hz CPU-upscale path and its frozen-on-
Deck fallback are deleted — the generated SkSL is compile-tested);
titles/scenes shape through textlayout (CJK-safe). Poster art streams
in as encoded bytes through the shared model and decodes renderer-side.

The session binary wires --browse host[:port] [--mgmt PORT]: KnownHosts
lookup (unpaired renders the pair-first scene), library + art fetch on
threads, PUNKTFUNK_FAKE_LIBRARY dev hook, and a session_params helper
shared with --connect. The minimal build refuses --browse cleanly.

Co-Authored-By: Claude Fable 5 <noreply@anthropic.com>

clients/linux-session/README.md

@@ -7,8 +7,15 @@ presenter of the Linux client re-architecture (punktfunk-planning:
 
 ```
 punktfunk-session --connect host[:port] [--fp HEX] [--launch id] [--fullscreen] [--stats]
+punktfunk-session --browse host[:port] [--mgmt PORT] [--fullscreen]
 ```
 
+`--browse` opens the console game library (the Skia coverflow over the animated aurora)
+instead of connecting: A launches the focused title as a stream in the same window,
+session end returns to the library, B quits (Gaming Mode returns). Paired hosts only —
+pairing is the desktop client / Decky plugin's job. `PUNKTFUNK_FAKE_LIBRARY=<file.json>`
+feeds canned entries with no host (portrait paths starting with `/` load from disk).
+
 Reads the same identity / known-hosts / settings stores as the desktop client
 (`punktfunk-client`) — pair there (or via its headless `--pair`) first; this binary never
 connects to a host it has no pinned fingerprint for (`--fp HEX` overrides the store).