feat: install release builds and report missing FFmpeg

Add make release and make install PREFIX=/Users/valdemar/.local. Keep optimized no-debug release artifacts separate; install adjacent CLI/app under lib/terebi and link bin/terebi. Preflight FFmpeg/pkg-config before compiling or installing, including cached builds.

Record the player's exact linked FFmpeg ABI paths. AppKit-only CLI/bootstrap validate native loadability and transitive dependencies before entering the FFmpeg-linked terebi-player. CLI fails with status 69 and remediation; Finder bootstrap shows a native alert and execs the player without losing initial events or process identity.

Verified staged installation with spaces, reinstall preservation, absent build dependencies, missing/corrupt/transitively broken dylibs, real modal error surface, installed CLI and Finder startup across exec, local/YouTube resume and window reuse, and full make check.

Sources/CLI/TerebiCLI.swift

@@ -20,6 +20,9 @@ enum TerebiCLI {
             }
             let app = executable.resolvingSymlinksInPath().deletingLastPathComponent()
                 .appendingPathComponent("terebi.app", isDirectory: true)
+            if let error = FFmpegRuntime.error(for: app) {
+                fail(error, code: 69)
+            }
             let configuration = NSWorkspace.OpenConfiguration()
             do {
                 // Launch without media first so SwiftUI creates its singleton window.