fix(gui): embed plot on EnSight import, in-panel channel switching, source-agnostic cue

[ahmadomira]

Summary

Fixes three issues on the plate-reader import path that surfaced after the EnSight reader landed. All three are GUI-layer; the reader is untouched. Stacks on feat/reader-ensight.

1. Plot detached from the tab after EnSight import

The plot overlapped the sidebar, couldn't be resized smaller, and floated above the Fit Curve tab. Cause: the EnSight path ran a modal QInputDialog mid-load_file, before data_loaded fired — a nested event loop during the first layout pass, unlike the BMG/txt paths. The plot widget is never reparented in code; the modal was the only structural divergence. Fix: remove the mid-load modal so every import path is identical (parse → build MeasurementSet → emit). A new regression test (test_fitting_session_layout.py) asserts the plot stays at stack index 0 and never becomes a top-level window, across load + channel switch.

2. Missing-concentrations popup → source-agnostic inline cue

The old popup hardcoded "BMG" even for EnSight, was verbose, and interrupted every import. Fix:

• Deleted the modal (gui/dialogs/bmg_prompt_dialog.py removed; no other callers).
• The Data panel shows a one-line inline banner that names the actual format, derived from metadata (ensight_metadata → "EnSight", bmg_metadata → "BMG", else generic) — never hardcodes one. It auto-focuses the concentration table and auto-clears once real values are entered.
• The fit-time guard stays (it only fires on a fit attempt, so it doesn't interrupt import) but is reworded source-agnostically.

3. In-panel channel switching (no re-import)

The reader already parses all channels into one frame; the load-time picker discarded all but one. Fix: the panel keeps the full multi-channel frame in memory and adds a Channel combo (disabled unless >1 channel) that rebuilds the MeasurementSet per selection — no file re-read. The concentration vector + unit carry across switches (all channels share the same plate columns); signals, fit results, and outlier/active-replica state reset via the existing data_loaded handler. Keyed off the presence of a channel column, so any future multi-channel reader gets the dropdown for free.

Test plan

• pytest tests/unit/gui/ tests/unit/test_ensight_reader.py tests/unit/test_io*.py — 128 passed, 6 skipped
• New: DataPanel tests for combo enable/disable, channel switch (signals change, entered concentrations preserved, placeholders adopted while pending), banner show/hide + source naming; full-load_file EnSight integration; plot-embed layout regression guard.
• Headless FittingSession check: plot stays embedded (stack idx 0, not a window) through EnSight load and channel switch; combo enabled with 3 channels; banner shown; 8×12 MeasurementSet.
• Manual: import an EnSight file — no modal, plot embeds normally, Channel dropdown lists channels, banner names "EnSight"; enter concentrations then switch channels (values persist); import BMG (banner names "BMG", combo disabled) and txt (no banner, combo disabled).

[Copilot]

Pull request overview

Fixes three issues in the plate-reader GUI import path that surfaced after the EnSight reader landed: (1) removes a mid-load modal QInputDialog that was detaching the plot widget from its stacked container, (2) replaces the BMG-hardcoded modal warning with a source-agnostic inline banner derived from metadata, and (3) adds in-panel channel switching that keeps the full multi-channel frame in memory and rebuilds the MeasurementSet per selection without re-reading the file.

Changes:

• DataPanel.load_file no longer runs a modal mid-load; the panel keeps _multi_channel_df and _channels and exposes a Channel combo (enabled only when >1 channel) that triggers _on_channel_changed to rebuild the MeasurementSet, carrying over user-entered concentrations when no placeholder flag is set.
• A new _placeholder_banner and _placeholder_source_name provide a source-agnostic inline cue; gui/dialogs/bmg_prompt_dialog.py and FittingSession._maybe_show_bmg_prompt are removed in favor of a status-bar mirror and the existing fit-time guard (also reworded source-agnostically).
• New tests: tests/unit/gui/test_fitting_session_layout.py regression-guards plot embedding through load and channel switch; tests/unit/gui/test_data_panel.py adds combo/banner/integration coverage including the real EnSight fixture.

Reviewed changes

Copilot reviewed 5 out of 5 changed files in this pull request and generated no comments.

Show a summary per file

File	Description
gui/widgets/data_panel.py	Removes mid-load QInputDialog; adds multi-channel state, Channel combo, _slice_channel/_make_ms/_on_channel_changed, inline placeholder banner, source-agnostic naming helper.
gui/fitting_session.py	Drops _maybe_show_bmg_prompt/modal; mirrors placeholder hint in status bar; reworded source-agnostic fit-time guard.
gui/dialogs/bmg_prompt_dialog.py	Deleted (no remaining callers).
tests/unit/gui/test_data_panel.py	Adds TestChannelCombo, TestPlaceholderBanner, TestEnsightLoadIntegration covering combo enablement, channel switch behavior (signals change, entered concentrations preserved, placeholders adopted), banner show/hide and source naming, and full load_file on real fixture.
tests/unit/gui/test_fitting_session_layout.py	New regression: plot widget remains at stack index 0, non-window, parented by _plot_stack before/after EnSight load and channel switch.

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[ahmadomira]

Squash-integrated into feature/io-readers as eee1602 (combined with the EnSight reader, rebased onto current main). Closing in favour of the integration branch.