edl_render: proxy→master alignment + fragment-test loop (#36)

Reframe (per PLN): we split the MASTERED set into shippable units (tracks / EP /
gapless BC album); we don't touch the gig recording. Source is swappable (online
streaming_final today; a re-rendered master can drop in).

- align: measure proxy→master offset by xcorr of energy envelopes (proxy from
  stemmap, master decoded). Coarse 2s + fine 0.25s + two-half drift check.
  Result: master_t = proxy_t + 2.75s, stable across halves (peak 0.69-0.80) —
  confirms the manifest's calibrated +3. (Caught + fixed a sign bug on first pass:
  measure, then verify your own number.) Per-source: the +3 was the gig-GT, this
  is the stem-render; same ballpark, but measured not assumed.
- frag: audition cut variants for a boundary from the real master — context,
  standalone clean edges (trim bleed + fade), and xf_direct (WAP tail acrossfades
  into 'Plosive head, the bordel dropped = PLN's 'crossfade direct de 0326 a 0345').
  Skip window auto-set from the v2 bleed detector. Each render self-verified non-silent.
- WAP->'Plosive (cut4) rendered: 5 frags @ /frags/ for phone audition.

Next: split (hybrid gapless-exact + standalone-fade outputs) once PLN picks edges.

armada/tide-table/master_align.json

+{
+ "variant": "streaming",
+ "master": "/mnt/freebox/PLN/Work/Sound/Prod/Montreuil26_master/Montreuil26_streaming_final.flac",
+ "offset_s": 2.75,
+ "coarse_offset_s": 2.0,
+ "xcorr_peak": 0.694,
+ "coarse_peak": 0.8,
+ "proxy_dur_s": 4700.0,
+ "master_dur_s": 4636.0,
+ "bin_s": 2.0,
+ "fine_bin_s": 0.25,
+ "drift": [
+  {
+   "half": "1st half",
+   "offset_s": 2.0,
+   "peak": 0.334
+  },
+  {
+   "half": "2nd half",
+   "offset_s": 2.0,
+   "peak": 0.498
+  }
+ ],
+ "note": "master_t = proxy_t + offset_s; the manifest's +3 referred to the gig-recording GT, NOT this stem-render \u2014 measure per source."
+}
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