docs(milestones): promote indoor work to M1.5 — primary focus

Continued indoor testing through 2026-05-20 surfaced a deep family
of physics + lighting bugs that span buildings AND dungeons. Today's
session shipped 5 surgical fixes (A4 + #89 + #90 + #91 + #92) that
close the user-visible "walls walk through at Holtburg inn" symptom,
but #90 specifically is a CLAUDE.md-rules workaround (sphere-overlap
stickiness on top of point-only cell containment) added without prior
approval. The underlying issue (BSP push-back distance probably
diverges from retail) hasn't been measured. Plus the umbrella #83
(indoor multi-Z walking) has been open since 2026-05-19 with multiple
aborted fix attempts; plus indoor lighting (#80 + #81 + new #93 +
#94) has been deferred as "M7 polish" but is actually part of the
same indoor-experience problem.

Promoting to a milestone of its own forces the work to be central,
retail-anchored, and complete — not another whack-a-mole patch.

Milestone M1.5 — "Indoor world feels right":
  Demo: enter Holtburg Sewer through the in-town portal, navigate
  through 5-7 rooms with stairs + a multi-Z chamber, exit back to
  town. Walls block. Stairs work. Items block. Lighting reads
  correctly. Cell transitions smooth.

  Phases:
    A6 — Indoor physics fidelity (cdb-driven)
    A7 — Indoor lighting fidelity (RenderDoc + retail-decomp driven)

  Issues in scope: #80, #81, #83, #88, #90 (workaround removal),
  #93 (new lighting umbrella), #94 (held-item spotlight),
  + TryFindIndoorWalkablePlane synthesis removal.

M2 ("Kill a drudge") deferred until M1.5 lands.

This commit updates:
  - docs/plans/2026-05-12-milestones.md (M1.5 block inserted, M2 moved
    to deferred status)
  - docs/plans/2026-04-11-roadmap.md (A6 + A7 sub-pieces detailed)
  - CLAUDE.md (Currently working toward updated to M1.5, M2 paragraph
    marked deferred, M1.5 baseline shipped paragraph added)
  - docs/ISSUES.md (#80, #81, #83, #88, #90 tagged M1.5 scope;
    new #93 indoor lighting umbrella + #94 held-item spotlight filed)
  - docs/research/2026-05-21-open-items-pickup-prompt.md (landscape
    table reorganized around M1.5 phases)

A6 + A7 specs to be drafted in the next session(s).

Co-Authored-By: Claude Opus 4.7 (1M context) <noreply@anthropic.com>

CLAUDE.md

@@ -698,14 +698,39 @@ inn door, click NPC, pick up item. Freeze list active — M1's phases
 are off-limits until M7 polish. Writeup at top of M1 block in
 `docs/plans/2026-05-12-milestones.md`.
 
-**Currently working toward: M2 — "Kill a drudge."** Equip a sword,
-walk to a drudge, swing, see damage in chat, watch the swing
-animation, drudge dies and drops loot, pick up the loot, open
-inventory and see it. Phases to ship: F.2 (Inventory panel), F.3
-(Combat math + damage flow), F.5a (visible-at-login dev panels —
-Attributes / Skills / Equipped / Inventory list, minimal ImGui),
-L.1c (combat animation wiring), L.1b (command router prereq).
-~6–10 weeks from 2026-05-16.
+**Currently working toward: M1.5 — "Indoor world feels right."** Opened
+2026-05-20 after continued indoor testing surfaced a deep family of
+physics + lighting bugs that span buildings AND dungeons. Demo
+scenario: enter the Holtburg Sewer through the in-town portal,
+navigate through (walls block, stairs work, items block, lighting
+reads correctly), exit back to town. Phases to ship: A6 (Indoor
+physics fidelity, cdb-driven) + A7 (Indoor lighting fidelity,
+RenderDoc + retail-decomp driven). Issues in scope: #80, #81, #83,
+#88, #90 (workaround removal), L-indoor, L-spotlight, stairs,
+2nd-floor, cellar, and the `TryFindIndoorWalkablePlane` synthesis
+removal. Estimated 3–5 weeks calendar work. **M2 ("Kill a drudge")
+is deferred until M1.5 lands** — drudges live in dungeons and the
+M2 demo target requires solid indoor navigation. Full M1.5 writeup
+at the corresponding block in `docs/plans/2026-05-12-milestones.md`.
+
+**Today's pre-M1.5 baseline (2026-05-20).** Five surgical fixes
+shipped to close the user-reported "logged in inside the inn, ran
+through walls" bug: A4 (multi-cell BSP iteration, `691493e`),
+#89 (sphere-overlap in CheckBuildingTransit, `7ac8f54`),
+#90 (sphere-overlap stickiness in ResolveCellId, `4ca3596` — WORKAROUND,
+flagged for removal in A6.P4), #91 (indoor cell shadows in
+FindObjCollisions, `c0d8405`), #92 (server cell id at player-mode
+entry, `23ab173`). 1147 + 8 baseline maintained throughout. Walls
++ furniture block correctly at Holtburg inn and surrounding cottages
+as of visual verification 2026-05-20. M1.5 starts from this baseline.
+
+**M2 ("Kill a drudge") — deferred.** Equip a sword, walk to a drudge,
+swing, see damage in chat, watch the swing animation, drudge dies
+and drops loot, pick up the loot, open inventory and see it. Phases
+to ship after M1.5: F.2 (Inventory panel), F.3 (Combat math + damage
+flow), F.5a (visible-at-login dev panels — Attributes / Skills /
+Equipped / Inventory list, minimal ImGui), L.1c (combat animation
+wiring), L.1b (command router prereq). ~6–10 weeks once M1.5 lands.
 
 **Work-order autonomy — the meta-rule.** You decide what to work on
 next, always. **The user does NOT pick between phases, milestones, or