feat(emit): show for-ancestry and description on sequence lifelines

[JonathanTurnock]

What

Sequence-diagram lifeline head cards previously showed only kind + name. A container/component lifeline gave no clue where it belongs, and dropped the node's /// description that C4 cards show.

Now each lifeline head shows:

• Dimmed for-ancestry (enclosing node names, outermost first) beneath the name — for container/component only.
• The /// summary, wrapped (≤2 lines + ellipsis) and dimmed, like a C4 card — for every declared lifeline.

Synthesised initiators (client/scheduler/event/caller) carry neither.

Applied to both renderers — the static SVG emitter and the web-IDE svelte-flow canvas — via the one shared layout engine, so they stay byte-aligned. Card height is computed dynamically so the taller head clears the lifelines/messages.

How

The FQN is module-flat (batch::SagaSweeper, not …::Batch::SagaSweeper), so the ancestry is walked from the graph's for parent chain in the projection, then threaded through the layout IR to both render edges.

Layer	Change
emit/scene.rs,project.rs	Lifeline gains summary+parent_path; ancestry_path walks the for chain (cycle-guarded)
layout/text.rs	wrap_desc — 2-line wrap + ellipsis, mirroring the C4 card
layout/sequence/*	IR fields + dynamic uniform card height (head geometry module shared with the renderer)
emit/render.rs	draws the dimmed parent path + summary under the name
wasm/lib.rs	outline exposes summary so the IDE's depth-collapse resolves the collapsed node
web-ide	threads summary + recomputes ancestry on collapse; SequenceLifeline.svelte renders the two dimmed lines
LANG.md §9.2	normative clause for the head-card content

Verification

• SVG, real sample (batch::SagaSweeper::sweep): components show kind / name / dimmed AcmePay::Batch / 2-line summary; scheduler initiator carries neither.
• Rust: 211 passed / 0 failed; cargo clippy --all-targets clean; cargo fmt applied.
• Web: 76 vitest pass (incl. new sequence.test.ts for collapse ancestry/summary); svelte-check 0 errors.
• WASM rebuilt (npm run build:wasm); regenerated pds-wasm_bg.wasm included.

🤖 Generated with Claude Code

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