Add basic interferogram+coherence workflow, v1 of web UI, isce2 comparison notebook

.gitattributes

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 # SCM syntax highlighting
 pixi.lock linguist-language=YAML linguist-generated=true
+src/sweets/web/frontend/package-lock.json linguist-generated=true

.gitignore

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 *.egg-info
 .DS_Store
 *.pdf
+docs/ifg_workflow_executed.*

docs/ifg-workflow-test-guide.md

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+# Running the IFG Workflow: Test Guide
+
+Quick reference for testing the `IfgWorkflow` on OPERA CSLC data.
+
+## 1. Create a config YAML
+
+The minimum config for an OPERA CSLC run:
+
+```yaml
+work_dir: /path/to/output/dir
+bbox:
+  - -118.2295   # xmin (west)
+  - 34.7939     # ymin (south)
+  - -116.5642   # xmax (east)
+  - 35.8195     # ymax (north)
+
+search:
+  kind: opera-cslc
+  out_dir: data
+  bbox: [-118.2295, 34.7939, -116.5642, 35.8195]
+  start: "2025-04-01T00:00:00"
+  end: "2025-06-01T00:00:00"
+  relativeOrbit: 64
+  # Optional: pin burst IDs instead of deriving from bbox each run
+  burst_ids:
+    - t064_135521_iw1
+    - t064_135521_iw2
+    # ... (use opera_utils.get_burst_ids_for_frame(frame_id) to list them)
+
+network:
+  max_bandwidth: 2   # nearest-2 network (each date connects to 2 neighbors)
+
+crossmul:
+  lines_per_block: 512
+
+stitch:
+  run_stitch: true
+  crop_to_bbox: true
+  run_burst_align: true   # remove inter-burst seam artifacts
+  burst_align_degree: 0   # 0 = constant offset per burst; 1 = planar ramp
+
+unwrap:
+  run_unwrap: false
+
+overwrite: false
+```
+
+To get the burst IDs for a known OPERA DISP frame:
+
+```python
+from opera_utils import get_burst_ids_for_frame
+print(get_burst_ids_for_frame(16941))
+```
+
+## 2. Run the workflow
+
+```bash
+python -m sweets ifg-run sweets_ifg_config.yaml
+```
+
+### Re-running from a specific step
+
+```
+Step 1 — DEM/watermask download + CSLC download
+Step 2 — Geometry stitching (LOS east/north/incidence angles)
+Step 3 — Crossmul (per-burst complex IFGs + coherence)
+Step 4 — Stitch (burst alignment + merge_by_date + wrapped phase)
+Step 5 — Unwrap (snaphu, if enabled)
+```
+
+To skip download and re-run from crossmul onward:
+
+```bash
+python -m sweets ifg-run sweets_ifg_config.yaml --starting-step 3
+```
+
+To re-run only the stitch step (crossmul outputs already exist):
+
+```bash
+python -m sweets ifg-run sweets_ifg_config.yaml --starting-step 4
+```
+
+When re-running the stitch step, delete the existing stitched outputs first
+so `overwrite: false` does not silently reuse them:
+
+```bash
+find <work_dir>/interferograms/stitched -maxdepth 1 -name "*.tif" -delete
+```
+
+## 3. Output layout
+
+```
+<work_dir>/
+  dem.tif
+  watermask.tif
+  geometry/
+    los_east.tif  los_north.tif  incidence_angle.tif  ...
+  data/
+    <CSLCs>
+    static_layers/
+  interferograms/
+    t064_135521_iw1/
+      20250403_20250415/
+        20250403_20250415_ifg.tif          # complex64 crossmul output
+        20250403_20250415_coherence.tif
+    ...
+    stitched/
+      20250403_20250415_ifg.tif            # burst-aligned complex
+      20250403_20250415_coherence.tif
+      20250403_20250415_wrapped_phase.tif  # np.angle(ifg), derived after stitch
+      burst_aligned/
+        t064_135521_iw1__20250403_20250415_ifg.aligned.tif
+        ...
+```
+
+Key design decisions:
+- Crossmul saves **complex64** `_ifg.tif` (not wrapped phase) so that
+  `merge_by_date` interpolates real+imag independently, avoiding ±π
+  discontinuities at burst seams.
+- Wrapped phase is derived with `np.angle()` **after** stitching.
+- Burst alignment runs **per date pair** (27 bursts each), not across all
+  pairs at once — passing all pairs together caused same-geography bursts
+  from different epochs to be compared as "overlapping", producing garbage
+  corrections.
+
+## 4. Plot and QA
+
+```python
+from sweets.plotting import plot_ifg_pairs, save_ifg_qa_metrics
+from pathlib import Path
+
+stitch_dir = Path("<work_dir>/interferograms/stitched")
+
+# Thumbnail grid of wrapped phase + coherence
+plot_ifg_pairs(stitch_dir, max_pairs=13, output_path="ifgs.png")
+
+# Per-pair coherence metrics + JSON sidecar
+save_ifg_qa_metrics(stitch_dir, output_path="qa.png")
+```
+
+## 5. Test dataset (frame 16941)
+
+- **Frame**: OPERA DISP frame 16941, T064 ascending, S California / Mojave
+- **AOI**: `POLYGON((-118.2295 34.7939,-116.5642 34.7939,-116.5642 35.8195,-118.2295 35.8195,-118.2295 34.7939))`
+- **Dates**: 2025-04-01 to 2025-06-01 (13 acquisitions, 6-day repeat)
+- **Bursts**: 27 (9 frames × 3 IW subswaths)
+- **Data on**: `/Volumes/WD_BLACK_SN7100_4TB/Documents/Learning/sweets-testing/sweets-f16941/`
+- **Config**: `sweets_ifg_config.yaml` in the same directory