Add match structure (countdown, timer, scoreboard, banner, persistent stats) and capital-ship fleet polish

Match phases (autoload/match_manager.gd, world/game_modes/):
- New server-authoritative MatchManager loops PRE_MATCH (30s countdown,
  ships held invisible/uncollidable, flagships creep into formation) ->
  IN_PROGRESS (active GameMode's clock runs) -> POST_MATCH (winner
  banner, result reported to matchmaking-api) -> back to a fresh
  PRE_MATCH forever, matching the always-on server-pool model instead
  of kicking players to the menu at match end.
- Win-condition logic lives in a new GameMode abstraction (game_mode.gd
  base + team_deathmatch_mode.gd, the only mode so far) so a future
  mode is a new subclass plus one factory branch, no timer/scoreboard/
  banner code changes needed.
- Three new HUD pieces: match_timer.gd (countdown/clock), scoreboard.gd
  (hold-Tab two-team panel), match_banner.gd (winner banner).
- New MatchStats autoload tracks per-match kills/deaths by peer_id
  (including bots), hooked into kill_feed_manager's existing
  report_kill() call site.

Persistent stats (matchmaking-api/):
- Player gains kills/deaths/hours_played columns; new
  POST /matches/report endpoint (server-only, called once at
  POST_MATCH) upserts each real player's totals by callsign via a
  shared app/crud.py helper also used by the matchmaking-queue join
  path. GET /stats/{callsign} returns the new fields alongside mmr/
  wins/losses.

Capital-ship fleet polish (world/flagship.gd, world/world.gd,
ships/ship_movement.gd, autoload/game_config.gd):
- Flagship formations are now a clean vertical line (no per-ship
  position/rotation jitter) so play_creep_in()'s rigid-group tween
  reads as one disciplined fleet arriving together, rising from
  directly below (not a random compass direction) over the full 30s
  countdown.
- Fixed a real bug where the creep-in tween only ever played on the
  server -- MatchManager._run_pre_match() called straight into World,
  server-only code a remote client's own process never runs, leaving
  their flagships static all match. World now triggers it off
  MatchManager.phase_changed instead, which fires identically on every
  peer.
- Fixed a second bug (only reachable on a fresh server boot's very
  first spawn): a phase==PRE_MATCH check that's true even before the
  match loop has genuinely started that phase for the first time fired
  play_creep_in() with a bogus zero-duration tween, corrupting the
  target the real 30s tween read moments later -- flagships would
  settle 4000 units off from their intended formation slot and fire
  from there instead. Guarded on get_remaining_seconds() > 0 too.
- The held ship's camera now actively tracks its own team's flagship
  centroid every tick during the countdown (position_smoothing
  disabled for the hold, since it fights a manually-driven target and
  was the reason the fleet read as invisible) instead of sitting fixed
  and wide-angle; local offset/zoom/smoothing are explicitly reset on
  release so control handback doesn't inherit a stale camera transform.
- _apply_pre_match_hold()/_apply_respawn() now set _dead/
  _held_for_pre_match inside the RPC itself, not just in the
  server-only caller -- those flags never reached remote clients
  before, so WASD wasn't actually blocked for them during the hold.
- Ships now launch from a narrow point directly beneath their own
  flagship formation instead of a full-circle scatter around the spawn
  marker (which could land a spawn behind/inside a hull). Bumped
  flagship_defense_radius so it still comfortably reaches a player who
  flies a straight line to the enemy side without correcting for that
  new offset.

ISN gets a Stealth Corvette hull mixed into its flagship formation
(assets/images/ships/isn/), banner art renamed off opaque UUID
filenames to isn_banner.jpeg/orc_banner.jpeg.

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

overview/tech.md

@@ -75,10 +75,14 @@ diverged from the original plan below:
    then connects directly to the returned server IP/port
 
 Not yet built: session tokens (server IP/port are handed back unauthenticated
-— fine for local dev, not for a real deployment), and a real server pool —
-only one dev server is registered right now (auto-seeded on API startup);
-`POST /servers/register` exists for real servers to self-register/heartbeat
-but nothing calls it yet.
+— fine for local dev, not for a real deployment).
+
+Real server pool is now live: `NetworkManager.host_server()` calls
+`POST /servers/register` once on boot and re-heartbeats every 8s, reporting
+live player counts; a real server registering on the same (ip, port, mode)
+as one of the 3 demo-seeded rows just takes it over in place. A background
+sweep marks any server `offline` once its heartbeat goes stale (crash/kill
+without clean deregister). See `CLAUDE.md` item 16.
 
 ### Steam Integration