dashboard.css + docs: migrate topology indent + icon/pending prose (#712 batch 12)

dashboard.css carried many CSS WHY-blocks duplicating prose
already in docs/web-ui.md (after PRs #722/#724/#728/#776).
Substantive new migration: topology indent geometry. Remaining
cookies collapse to docs pointers.

Moved to docs/web-ui.md::Topology tree:
- Indent + lane geometry paragraph (~18 lines new prose):
  per-depth 1.8em ladder rationale + hardcoded six levels +
  CSS Values 5 attr() partial-support caveat (Chromium-only as
  of 2026) + lane center continuation bars + bottom: -0.4em
  prefix extension to merge sibling vertical lines + horizontal
  stub at icon midline.

Collapsed in dashboard.css:
- Topology indent block (#363/#361) → 3-line pointer
- Tree prefix lanes block (#388) → 3-line pointer
- Tree prefix depth-step ladder (~6 lines) → 4-line tighter
  paraphrase (lane-meets-icon rationale stays inline as it's
  immediate context for the values below)
- Live cards icon-left split (#177/#344) → 6-line tighter
  paraphrase + docs pointer
- Icon selection-toggle hover/focus (#443) → docs pointer
- Icon img absolute positioning (#177) → docs pointer
- Icon favicon fallback (#195/#202) → docs pointer
- Pending state queued vs running (#769) → docs pointer
- Icon-only nav strip (#262/#333) → 7-line tighter + docs pointer
- Approval requested-at chip (#272) → 2-line pointer
- In-flight step indicator (#437) → 4-line pointer
- M0V3 affordance (#486) → 3-line pointer
- Cancel-X queued (#575) → 5-line pointer

dashboard.css: 51 → 36 cookies (counting hex-color false positives;
~15 actual issue refs scrubbed). Net ~50 lines of CSS WHY-prose
collapsed to brief docs pointers; ~18 lines of new substantive
prose migrated to docs/web-ui.md::Topology tree.

docs/web-ui.md

@@ -538,6 +538,26 @@ needed). The joint at the row's own depth column is `├` (more
 siblings below) or `└` (last sibling at this depth — vertical
 stops at the row's icon midline).
 
+**Indent + lane geometry.** Each depth level shifts the row right
+by `1.8em` (the lane width). The per-depth ladders are hardcoded
+for six levels — enough for any plausible hive topology, and the
+typed `attr()` function from CSS Values 5 that would collapse
+this to one rule is still partial-support (Chromium-only as of
+2026). The `.tree-prefix` span sits absolutely positioned with
+`left: -<depth>*1.8em` so its right edge meets the row content
+(the icon) and its leftmost lane lines up with top-level rows'
+icons at `x = 0`. Each `.tree-lane` is `flex: 0 0 1.8em` so all
+lanes have equal width. Continuation bars are drawn at lane
+center (`left: 0.6em`, `border-left: 1px solid currentColor`,
+`top: 0; bottom: 0`) and extend through `.containers { gap: 0.4em }`
+into the next sibling's prefix (`bottom: -0.4em` on the prefix
+span itself) so adjacent ancestor lines visually merge into one
+unbroken vertical line. The horizontal stub at a row's own joint
+lands at the icon midline so the L/T meets the icon edge cleanly.
+When every container has `parent = null` (pre-topology state) the
+`[data-depth]` attribute is absent on every row and these rules
+are no-ops — the layout reads exactly like the legacy flat list.
+
 ### Selection bar
 
 Per-card action buttons (`R3ST4RT` / `ST0P` / `ST4RT` / `R3BU1LD` /