Rework how a game starts: dev mode, a bare opening, and fleet growth

Adds a Dev Mode entry to the main menu and takes the play-testing
conveniences out of a normal game, which turn out to be the same change
from two directions.

DEV MODE. Banks 2000 of every resource, grants 500 research points, and
plants one of each planet type in the chunks around the spawn. Built ON TOP
of reset_new_game() rather than beside it, so a dev game is a normal game
plus a stock rather than a second definition of "fresh game" to keep in
sync. Offered only when running from Godot - OS.has_feature("editor"), the
tag an export clears - as is the map editor. Hidden AND guarded: pressing
either anyway is refused, because visibility is presentation and the rule is
the rule.

The menu now lays its stack out in code. Hiding two of four entries with
scene-authored offsets would leave holes in a shipped build - the same
failure the HUD columns had - so it measures the entries that actually exist
and centres on them.

A NORMAL GAME NOW HANDS OVER NOTHING. No 500 banked ore (removed from both
reset_new_game and the autoload's own default, so the two cannot disagree),
and no gas giant guaranteed in the origin chunk. Both were play-testing
conveniences that had become part of the real world's shape: every player
got the same landmark in the same place. Play-testing wanted all four planet
types anyway, and a normal game wanted none of them - different needs, now
different mechanisms.

WorldGen cannot read GameState back (an autoload is not resolvable as a
global identifier that early, the hazard PlanetSetups.gd already works
around), so GameState.dev_mode's setter PUSHES the flag down. World
generation stays static and dependency-free, GameState stays the single
source of truth, and dev planting is applied after every rng draw so a dev
world and a normal one differ only in those four chunks.

FLEET SIZE. BASE_FLEET_SIZE was doing two jobs - how many slots exist AND
how many ships you start with - which forced a new game to open with a full
fleet, leaving the first ship crafter nothing to do. Split into
BASE_FLEET_SIZE (3 slots) and STARTING_SHIP_COUNT (1 vessel), so the opening
has two empty slots to fill. A third copy of the old value turned up in
PlanetAtmosphereController, hardcoded as spawn_ships(5) and silently
degraded into "however many slots exist" once max_fleet_size() clamped it.

The doctrine branch now runs 3 -> 10 slots. Wing (30 -> 15) and Squadron
(70 -> 35, 2 -> 1 points) are cut hardest: they are no longer a mid-game
luxury but the ordinary way out of the opening, and pricing them as a luxury
made the early game feel stuck. Armada follows at 90/2. Two new tiers,
Battlegroup and Grand Fleet, grant +2 each - seven single-vessel nodes in
one lane would be a long monotonous chain for a branch that only ever does
one thing. DEFAULT_FORMATION grows to 10 slots, because max_fleet_size()
clamps to its length and a doctrine past that would charge real resources
for nothing; test_fleet_growth.gd asserts that invariant directly.

TEST FALLOUT, all of it from the deliberate change rather than a defect:

- Tests that silently inherited the old 5-ship default now ask for the fleet
  they need. Several had to crew it from their first frame rather than
  _initialize(), where the engine's deferred tree-entry finalization undoes
  it - the same hazard those tests already documented for set_process(false).
- test_planet_landing_proximity and test_return_position_matches_planet take
  the FIRST chunk holding a planet and land there. The guaranteed gas giant
  had been masking that this can now be a black hole, which destroys ships on
  contact. They exclude it, and clear the asteroids the field already placed.
- test_pivot_controls measured rotation with angle_difference, which wraps at
  +/-pi, so a hold that turned a full circle read as no rotation. Latent
  flakiness that only ever showed under load; it now reads the controller's
  unwrapped pivot_hold_amount.
- test_research_points was failing on ore, not points: can_unlock() checks
  the ore price too, and a fresh game banks nothing now.
- test_gas_system's "a reachable gas source near the spawn" premise moved to
  dev mode, which is where that guarantee now lives.

Full suite green at 97/97.

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

MainMenu.tscn

@@ -97,6 +97,33 @@ theme_override_font_sizes/font_size = 32
 horizontal_alignment = 1
 text = "Map Editor"
 
+[node name="DevModeButton" type="Control" parent="UI"]
+anchor_left = 0.5
+anchor_right = 0.5
+anchor_top = 0.5
+anchor_bottom = 0.5
+offset_left = -64
+offset_right = 64
+offset_top = 190
+offset_bottom = 318
+script = ExtResource("2")
+icon = 29
+glow_color = Color(1, 0.7, 0.25, 1)
+
+[node name="DevModeLabel" type="Label" parent="UI"]
+mouse_filter = 2
+anchor_left = 0.5
+anchor_right = 0.5
+anchor_top = 0.5
+anchor_bottom = 0.5
+offset_left = -200
+offset_right = 200
+offset_top = 324
+offset_bottom = 380
+theme_override_font_sizes/font_size = 32
+horizontal_alignment = 1
+text = "Dev Mode"
+
 [node name="StatusLabel" type="Label" parent="UI"]
 anchor_left = 0.5
 anchor_right = 0.5