feat: analysis providers, settings UI, song search, WAV duration fix

- Multi-provider AI analysis (Anthropic, OpenAI, Ollama, Algorithmic)
- server-only guards on all provider files; client bundle fix
- /settings page with provider status, Ollama model picker, preferences
- Song search box on /analyze replacing raw MBID input (debounced, keyboard nav)
- Auto-register song via MusicBrainz on POST /api/tracks (no more 404)
- Fix WAV duration bug: last section songEnd was double-counting elapsed time
- Registry sync comment updated for self-hosted HTTPS git servers

Co-Authored-By: Claude Sonnet 4.6 <noreply@anthropic.com>

lib/analysis/providers/algorithmic.ts

@@ -0,0 +1,131 @@
+import type { CTPDocument } from "@/lib/ctp/schema";
+import type { AnalysisInput, AnalysisProvider } from "@/lib/analysis/providers";
+
+// Section templates keyed by duration bucket
+interface SectionTemplate {
+  labels: string[];
+  weights: number[];
+}
+
+function getTemplate(duration: number): SectionTemplate {
+  if (duration < 120) {
+    return {
+      labels: ["Intro", "Verse / Chorus", "Outro"],
+      weights: [0.12, 0.76, 0.12],
+    };
+  }
+  if (duration < 240) {
+    return {
+      labels: ["Intro", "Verse", "Chorus", "Verse + Chorus", "Outro"],
+      weights: [0.08, 0.22, 0.20, 0.38, 0.12],
+    };
+  }
+  if (duration < 360) {
+    return {
+      labels: ["Intro", "Verse", "Chorus", "Verse + Chorus", "Bridge", "Outro"],
+      weights: [0.07, 0.20, 0.18, 0.33, 0.10, 0.12],
+    };
+  }
+  return {
+    labels: ["Intro", "Verse", "Chorus", "Verse + Chorus", "Instrumental", "Bridge", "Outro"],
+    weights: [0.06, 0.18, 0.16, 0.30, 0.10, 0.10, 0.10],
+  };
+}
+
+function buildFallback(input: AnalysisInput): CTPDocument {
+  return {
+    version: "1.0",
+    metadata: {
+      title: input.title ?? "Unknown Title",
+      artist: input.artist ?? "Unknown Artist",
+      mbid: input.mbid ?? null,
+      duration_seconds: input.duration,
+      contributed_by: input.contributed_by,
+      verified: false,
+      created_at: new Date().toISOString(),
+    },
+    count_in: {
+      enabled: true,
+      bars: 2,
+      use_first_section_tempo: true,
+    },
+    sections: [
+      {
+        label: "Song",
+        start_bar: 1,
+        bpm: input.bpm,
+        time_signature: { numerator: 4, denominator: 4 },
+        transition: "step",
+      },
+    ],
+  };
+}
+
+export const algorithmicProvider: AnalysisProvider = {
+  id: "algorithmic",
+  label: "Algorithmic (no AI)",
+  type: "algorithmic",
+
+  async isAvailable() {
+    return { available: true };
+  },
+
+  async generateCTP(input: AnalysisInput): Promise<CTPDocument> {
+    try {
+      const { bpm, duration, title } = input;
+
+      const totalBars = Math.floor((duration * bpm) / 240);
+      const template = getTemplate(duration);
+      const { labels, weights } = template;
+
+      // Allocate bars per section
+      const rawBars = weights.map((w) => Math.round(totalBars * w));
+
+      // Adjust last section so total is exact
+      const allocatedSum = rawBars.reduce((a, b) => a + b, 0);
+      const diff = totalBars - allocatedSum;
+      rawBars[rawBars.length - 1] = Math.max(1, rawBars[rawBars.length - 1] + diff);
+
+      // Determine time signature
+      const lowerTitle = title?.toLowerCase() ?? "";
+      const numerator = lowerTitle.includes("waltz") || lowerTitle.includes("3/4") ? 3 : 4;
+      const timeSignature = { numerator, denominator: 4 as const };
+
+      // Build sections with cumulative start_bar
+      let currentBar = 1;
+      const sections = labels.map((label, i) => {
+        const start_bar = currentBar;
+        currentBar += rawBars[i];
+        return {
+          label,
+          start_bar,
+          bpm,
+          time_signature: timeSignature,
+          transition: "step" as const,
+        };
+      });
+
+      return {
+        version: "1.0",
+        metadata: {
+          title: input.title ?? "Unknown Title",
+          artist: input.artist ?? "Unknown Artist",
+          mbid: input.mbid ?? null,
+          duration_seconds: duration,
+          contributed_by: input.contributed_by,
+          verified: false,
+          created_at: new Date().toISOString(),
+        },
+        count_in: {
+          enabled: true,
+          bars: 2,
+          use_first_section_tempo: true,
+        },
+        sections,
+      };
+    } catch {
+      // Algorithmic provider must never surface an error
+      return buildFallback(input);
+    }
+  },
+};