feat(playground): image & video generation tabs + real chat metrics

The infosave collection now ships media models (Lumina-Image-2.0, MiniMax-H3
Turbo) that cortiq runs via `imagine`/`animate` CLI, not `cortiq serve`. The
gateway grows a media API: local .cmf files are classified by `cortiq info`
(chat/image/video, cached), generations run as tracked jobs with step progress
parsed from stdout, one at a time, cancellable, outputs under <data>/media.

The playground becomes three tabs. Image: width/height/steps/CFG/seed, live
progress, result rendered from P6 PPM to a canvas in the browser (PNG export
via toBlob). Video: frames/steps/quality/seed plus optional first/last
keyframes (rasterized to PPM client-side); the MJPEG+PCM AVI is decoded in JS
and played on a canvas synced to the wav — no ffmpeg on either side (mp4 remux
happens opportunistically when ffmpeg exists). A metrics card shows resolution,
steps, seed, total time, time per step/frame and file size.

Chat metrics: the local cortiq server sends no usage chunk in streams, so
token counts showed 0/0. tap_stream now injects one OpenAI-shaped usage event
ahead of [DONE] with the gateway's ~4-chars/token estimate, flagged
`cortiq_estimated`; the UI renders it as "≈ N / M" and adds tok/s and
time-to-first-token. Registration skips media packs (a `cortiq serve` entry
for a diffusion model would only fail) in both Register and the wizard's
Finish.

36 new UI strings translated across all 7 languages.

web/js/i18n/en.js

@@ -461,4 +461,42 @@ export default {
   "onboarding.deleteFile": "Delete the .cmf file from disk",
   "onboarding.confirmDelete": "Delete '{id}'? The .cmf file will be removed from disk.",
   "onboarding.unregistered": "Also unregistered: {ids}",
+
+  // playground: media generation + streaming metrics
+  "pg.tab.chat": "Chat",
+  "pg.tab.image": "Image",
+  "pg.tab.video": "Video",
+  "pg.generate": "Generate",
+  "pg.generating": "Generating…",
+  "pg.genFailed": "Generation failed — see the log.",
+  "pg.result": "Result",
+  "pg.genMetrics": "Generation metrics",
+  "pg.imagePromptPlaceholder": "a red fox sitting in snow at sunset, photorealistic, detailed fur",
+  "pg.videoPromptPlaceholder": "a corgi in a chef hat flipping a pancake, sizzling sounds and a cheerful bark",
+  "pg.imageEmpty": "The generated image will appear here.",
+  "pg.videoEmpty": "The generated clip (with audio) will appear here.",
+  "pg.width": "Width",
+  "pg.height": "Height",
+  "pg.steps": "Steps",
+  "pg.seed": "Seed",
+  "pg.randomSeed": "Random seed",
+  "pg.cfgHint": "Guidance scale; ≤ 1 disables CFG and halves the work.",
+  "pg.frames": "Frames",
+  "pg.framesHint": "At 24 fps; snapped to the model's grid.",
+  "pg.quality": "JPEG quality",
+  "pg.videoSizeHint": "Multiples of 32; the trained short edge is 768.",
+  "pg.videoStepsHint": "The Turbo LoRA is trained for 4 steps.",
+  "pg.firstFrame": "First frame (optional)",
+  "pg.lastFrame": "Last frame (optional)",
+  "pg.keyframeHint": "Turns the run into keyframe-to-video.",
+  "pg.resolution": "Resolution",
+  "pg.genTime": "Generation time",
+  "pg.timePerStep": "Per step",
+  "pg.timePerFrame": "Per frame",
+  "pg.fileSize": "File size",
+  "pg.duration": "Duration",
+  "pg.play": "Play",
+  "pg.noMediaModels": "No local {kind} model yet. Download one (e.g. from the infosave collection) in Import:",
+  "pg.tokSpeed": "Speed",
+  "pg.ttft": "First token",
 };