Extract hand-rolled progress meter into shared ui/ProgressBar

[atomantic]

Summary

Six surfaces had each re-implemented the same h-1.5 rounded-full track + style={{ width: ${pct}% }} fill, and they had already drifted on accessibility — only two carried role="progressbar" with aria-valuenow, so the rest were invisible to a screen reader.

• Adds client/src/components/ui/ProgressBar.jsx. It always emits the ARIA trio (role="progressbar", aria-valuenow, aria-valuemin, aria-valuemax) plus an accessible name from label, which defaults to Progress so a bar is never nameless.
• Knobs map to real call-site shapes, nothing speculative: percent (clamped 0..100), tone (accent / accent2 / success / warning / error / muted), label, size (sm h-1.5, md h-2), track (bg on a card, border on the page ground), duration (static Tailwind class map — an interpolated duration-${n} is invisible to the build), and className for layout only.
• percent follows the repo's sentinel rule: null/undefined means unmeasurable and draws the indeterminate pulse with no aria-valuenow (the LoRA installer gets no Content-Length from some mirrors), while a non-finite number is a broken measurement (a 0 / 0 ratio) and renders an empty determinate bar rather than silently claiming indeterminate.

Migrated call sites — no behavior change beyond the added ARIA:

File	Meter
client/src/pages/Loras.jsx	HuggingFace byte-level download (determinate + indeterminate)
client/src/components/pipeline/manuscript/ManuscriptReadAloud.jsx	narration elapsed/total
client/src/components/pipeline/stages/EpisodeVideoStage.jsx	scenes accepted
client/src/components/meatspace/post/PostLlmDrillRunner.jsx	prompt counter, training counter, countdown timer
client/src/components/meatspace/post/MemoryPractice.jsx	practice position, per-chunk mastery
client/src/components/pipeline/AutopilotMilestones.jsx	overall milestone meter

The two files that had a local component literally named ProgressBar keep a thin domain wrapper over the shared primitive — PromptProgress (the "Prompt N of M" counter) and PracticeProgress — so the shared meter is the only thing drawing a bar. Consolidating the drill runner's training block into PromptProgress removed a seventh near-duplicate copy.

Two cosmetic values were normalized as part of de-drifting: the drill runner's two /60-opacity fills are now solid semantic tones, and the read-aloud track is rounded-full like the other five instead of rounded.

Also adds client/src/components/ui/README.md — the directory had no catalog, which is a large part of why six copies of this markup existed. It indexes every primitive in the directory and states the rule that a new one gets a row.

Closes #4138

Test plan

• New client/src/components/ui/ProgressBar.test.jsx (29 cases): ARIA trio + accessible name, the default name when a host omits label, fill width, clamping above 100 / below 0, rounded aria-valuenow with a fractional width preserved, NaN/Infinity reading as an empty determinate bar rather than the indeterminate pulse, null/undefined producing the pulse with no aria-valuenow but with the bounds intact, every tone class, unknown-tone fallback, size/track switching, className pass-through, and the static duration map with its fallback.
• cd client && npm test — 640/641 files pass. The one failure is src/pages/MoodBoardDetail.test.jsx (a GalleryImagePicker act-warning flake unrelated to this change: it touches no progress meter, and the file passes on its own re-run).
• npx biome lint --error-on-warnings clean on all eight touched files.
• src/a11yConventions.test.js passes.