feat(prune): R3 guarded deletion — confirm-to-delete + panel button

Extend BANK_PRUNE_FOLDER from report-only to dry-run→confirm-with-manifest→
delete exactly the pure-core orphan set (fresh recompute, stale entries skipped).
Windows routes to Recycle Bin (SHFileOperation+FOF_ALLOWUNDO), else unlink.
New pure prune_button module + footer button dispatching the action id. No
ext-state write, no undo point (deletion is not REAPER-undoable).

src/persist.h

@@ -195,6 +195,38 @@ public:
     // folder on disk yet — an unsaved or never-captured project has nothing to reclaim.
     PruneReport pruneDryRun() const;
 
+    // The FULL (untruncated) prune orphan set for the ACTIVE project — the same fresh
+    // enumerate + pure-core compute pruneDryRun() runs, but returning EVERY orphan (no
+    // 64-cap display clip) as project-relative index-spelled paths, in enumeration order.
+    // The R3 action calls this to obtain the exact set it will CONFIRM and then delete
+    // (pruneDryRun's truncated list is for the console readout; the delete set must be
+    // complete). READ-ONLY — no ext-state, no save, no file mutation. Empty when there is
+    // no active/saved project or no bank folder yet.
+    std::vector<std::string> pruneOrphanSet() const;
+
+    // Phase R (Reclaim), R3: DELETE the confirmed orphan set — the SOLE file-deletion path
+    // in ReaSampler, callable ONLY after an explicit user confirm of a specific manifest.
+    // Given the orphan set the user was shown and confirmed (`confirmed`, typically the
+    // full pruneOrphanSet() captured moments earlier), this re-enumerates the folder, runs
+    // the pure core FRESH, and deletes exactly `confirmed ∩ freshOrphans` (pruneDeletePlan)
+    // so a file that vanished or became referenced between confirm and delete is skipped,
+    // never wrongly deleted — and a newly-appeared orphan the user did NOT see is never
+    // swept. Deletion routes to the OS trash where a portable move-to-trash is verified
+    // (Windows Recycle Bin via SHFileOperation + FOF_ALLOWUNDO); elsewhere it falls back to
+    // std::filesystem unlink behind this confirm guardrail (see persist.cpp for per-platform
+    // routing). Non-throwing: every filesystem call uses error_code forms; a per-file
+    // failure (locked, already gone) is recorded and skipped, never thrown across the C ABI.
+    //
+    // Does NOT modify the BankIndex/book (orphans are unreferenced by definition) and does
+    // NOT modify the OwnedFileManifest (a reclaimed file drops out of the (owned ∩ present)
+    // algebra naturally once it is off disk — no persist write, so no undo-point question
+    // and no risk to the referenced/owned safety). Writes NO ext-state at all.
+    //
+    // No-ops (empty result) when there is no active/saved project, no bank folder, or the
+    // delete plan is empty (everything went stale). The caller is responsible for having
+    // shown the confirm; this method does NOT prompt.
+    PruneDeletionResult pruneReclaim(const std::vector<std::string>& confirmed) const;
+
     // Poll the active project. Detects a project load (active project changed)
     // and a Save-As (active project's .rpp path changed) and reacts accordingly.
     // Intended to be driven by REAPER's "timer" register. Idempotent per tick.