P1D.2C: bring Time Signals interaction to ArdIrec parity

[masarray]

Stacked on ARSAS P1D.2A consumer PR #297 (which itself is stacked on P1D PR #295). Keep this draft and do not merge until the engine dependency is rebased to merged ArdIrec main.

P1D.2C is the Time Signals workstation-parity slice. It deliberately does not implement the P1D.2B Measurement Panel, but consumes the additive P1D.2A semantics needed to make Time Signals authoritative.

Implemented in this slice:

• trigger-focused opening window: about 8 nominal cycles with trigger near 45% from the left;
• initial C1/C2 bracketing the trigger by one nominal cycle;
• normal wheel belongs to vertical track scrolling; Ctrl+wheel zooms time around the pointer;
• blank-plot drag pans; C1/C2 have visible draggable handles; right-click places C2;
• visible-edge snap during interaction plus exact native ArdIrec digital-edge snap on completed cursor placement when the capability is present;
• signal browser grouped as Voltage / Current / Other Analog / Digital Events using ArdIrec analog-role/phase semantics, with conservative unit fallback for older bridges;
• digital active bands respect COMTRADE normal_state, including active-low channels;
• large-record decimated plot points preserve their exact source-frame identities, fixing cursor-to-analysis mapping across multi-rate records;
• protection event rows come from retained actual transition metadata, so adaptive transition sampling cannot erase the event table;
• analysis fallback now resolves from the visible Time Signals center rather than the hidden legacy waveform viewport;
• collapsed legacy one-channel renderer is no longer loaded on every signal-row selection;
• Trigger view and Full record are explicit workstation actions.

P1D.2B remains responsible for the dedicated global measurement panel / representation UI. This PR keeps C1/C2 interaction and source identity ready for that context without duplicating the measurement presentation layer.