Documentation pass before context compaction

The roadmap was actively misleading: an earlier stage renumbering left Stage 2's
completed work sitting under a "Stage 3 -- todo" heading, and the inventory
table orphaned with no heading at all. Since that file is the primary handoff
document, a fresh session would have started by re-implementing accounts and
characters. Rewritten.

Captured in full, from the original brief rather than from memory, the two
stages not yet built:

- Stage 3 (inventory and loot): 4 slots, potions rare from trash and guaranteed
  from bosses, world-shared loot, and the player-instanced food item -- with a
  note that two loot visibilities must exist from the start, because proving the
  instanced path works is the food item's entire purpose.
- Stage 4 (upgrades): every upgrade with its exact stated effect, plus the two
  constraints it will collide with -- sniper's 2x bullet speed against the
  tunnelling threshold, and per-player bullet travel against the interest radius
  that test_interest.gd currently derives from static content.

Ten open questions are listed as explicitly do-not-guess, seven of them blocking
Stage 4.

ARCHITECTURE.md still claimed "the arena is a rectangle" and "no tilemap
collision", both untrue since Stage 1. Rewritten around MapGrid, with what the
grid costs (axis-aligned, 32px-quantised, bullets under a tile per tick) rather
than only what it buys.

Added a "verification traps" section to WORKFLOW.md recording six mistakes made
during this work, each of which cost a round trip of reporting something fixed
that was not: verifying the artefact rather than the behaviour, dumping the
wrong channel, measuring a configuration where the bug cannot exist, a test
whose setup silently invalidated it, git checkout reverting real work alongside
a probe, and a pattern edit matching in two files. They are specific enough to
be actionable.

Also documented the diagnostics in CLAUDE.md -- they were undiscoverable -- and
recorded the current verification surface so "everything passes" has a stated
meaning.

206 tests, 15 smoke assertions, both diagnostics pass.

CLAUDE.md

@@ -13,13 +13,25 @@ the obvious default.
 
 ```bash
 tools/check.sh      # parse-check every script (~5s) -- run after every edit
-tools/test.sh       # GUT suite, headless (~2s)
-tools/smoke.sh      # real server + 2 bot clients over ENet (~35s)
-tools/bench.gd      # godot --headless --path . --script tools/bench.gd
+tools/test.sh       # GUT suite, headless (~3s)
+tools/smoke.sh      # real server + 4 bot clients over ENet (~40s)
 tools/server.sh     # dedicated server
-tools/client.sh --join --name ada
+tools/client.sh --listen            # host and play, no menu
 ```
 
+Diagnostics. Each runs as a *scene* (they need the `Net` autoload) and exits
+non-zero on failure, so they gate like tests:
+
+```bash
+godot --headless --path . res://tools/diag_prediction.tscn    # prediction gap; injects clock drift
+godot --headless --path . res://tools/diag_progression.tscn   # kill -> xp -> level -> death -> roster
+godot --headless --path . --script tools/bench.gd             # sim cost per tick
+python3 tools/build_local_assets.py                           # rebuild the local-only bullet atlas
+```
+
+`diag_progression` exists because the bot smoke test cannot cover progression:
+bots are poor shots and rarely kill anything.
+
 Everything after `--` goes to `GameOpts.parse()`:
 
 | Flag | Effect |