feat: Implement history tracking with new CLI commands for viewing past transcripts and usage statistics.

docs/HISTORY_AND_STATS.md

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+# History and Stats Implementation Plan
+
+This document outlines the design and implementation of the `history` and `stats` features in Toak.
+
+## Data Storage
+All transcriptions will be stored in a JSON Lines (`.jsonl`) file located at `~/.local/share/toak/history.jsonl`.
+Since Toak uses Native AOT and JSON serialization needs source generation, we'll keep the model simple.
+
+**Entry Model:**
+```json
+{
+  "Timestamp": "2025-01-15T09:23:00Z",
+  "RawTranscript": "hello world",
+  "RefinedText": "Hello world.",
+  "SkillName": "Professional",     // null if default type/script
+  "DurationMs": 1500               // time taken for STT + LLM
+}
+```
+
+## `toak history` Command
+Provides access to past dictations.
+
+- `toak history` - Shows the last 10 entries.
+- `toak history -n <count>` - Shows the last `<count>` entries.
+- `toak history --grep <pattern>` - Filters the history entries matching the given keyword in the RefinedText (case-insensitive).
+- `toak history --export <file>` - Writes the output as a Markdown file.
+- `toak history --shred` - Deletes the `history.jsonl` file entirely.
+
+## `toak stats` Command
+Reads the `history.jsonl` file and outputs usage analytics using `Spectre.Console`.
+
+**Metrics:**
+- Total recording count
+- Total processing duration (sum of `DurationMs`)
+- Average processing duration
+- Most active day
+- Most frequently used skill (if any)
+
+## Architecture Changes
+1. **`HistoryManager.cs`**: Handles thread-safe appending `HistoryEntry` to the `.jsonl` file, reading, and clearing.
+2. **`DaemonService.cs`**: Calls `HistoryManager.SaveEntry` during the `ProcessStopRecordingAsync` method after text is finalized.
+3. **`HistoryCommand.cs` & `StatsCommand.cs`**: CLI command definitions.
+4. **`AppJsonSerializerContext.cs`**: Needs `[JsonSerializable(typeof(HistoryEntry))]`.