0.3.0 — Tactical mode port (engine, mode input on the tools, tactical goldens)

The tactical-mode port: the engine now covers both of upstream's engagement
plans. Orbit-mode behavior is unchanged — the orbit fixtures regenerate
byte-identically (their _meta.source_commit pin advances to upstream
843a2c5, the commit that introduced tactical mode without touching orbit
behavior).

Added

• Tactical mode in the engine (src/engine/tactical.ts plus a
  mode: "orbit" | "tactical" argument on Simulation / runEngagement,
  mirroring the browser's resetSim(seed, mode)): the multi-FPV sortie
  stream — per-seed launch plans and aim points, per-airframe EMCON keying,
  the pilot-station launch scheduler with commit holds, the strike/hunter
  FSM sharing the orbit attack run, and the sim's own STALEMATE end state
  (outcome reason packages_expended). Both modes share every RNG draw
  through emplacement; tactical results add the objective, per-airframe
  package state, sortie tallies and the killer id.
• mode input on the tools: run_engagement, sweep_seeds and
  compare_configs accept mode ("orbit" default); TACTICAL.* overrides
  (package size, pilot stations, reserve-or-retask, launch spacing,
  objective geometry — including the boolean RESERVE_HUNTER) join the
  validated parameter table and get_config_schema; describe_model gains
  a tactical_mode section; sweeps over tactical results add per-side
  strikes_delivered distributions.
• Second golden-fixture set (test/fixtures/golden-seeds-tactical.json,
  the six featured tactical seeds) with matching golden-master tests, and
  tactical coverage in the fixture generator. Parity for the port was
  additionally cross-checked against the vm-run original browser sim over
  seeds 1–500: outcomes, event logs, fix floats and per-airframe positions
  all match exactly, reproducing the documented 27% / 15% / 58% split.

Changed

• CI: the upstream-drift gate now regenerates and compares BOTH fixture
  sets, so a tactical-behavior change upstream (or an engine regression in
  either mode) is caught the same way orbit drift always was.

Docs

• README, DESIGN_NOTES.md and the pinned docs/upstream/DESIGN_NOTES.md
  copy re-synced for the two-mode era (SNAPSHOT.md pin: 843a2c5).