[Feature Request] /insights command needs date range filtering and comparison mode

Bug Description
Title: /insights — Add date range filtering and comparison mode

Problem: Running /insights always analyzes all sessions. There's no way to see what changed between two time periods, making it hard to track improvement
over time.

Proposed solutions (pick one or both):

1. Date range flag: /insights --since 2026-02-11 or /insights --from 2026-02-11 --to 2026-02-21 to scope the report to a specific period.
2. Diff/comparison mode: /insights --compare that automatically finds the last generated report and highlights what improved, regressed, or stayed the

same.

Use case: I run insights periodically to track my workflow improvements. Today's report includes everything from day one, so I can't tell what changed in
the last 10 days vs. the prior period.

Environment Info

• Platform: darwin
• Terminal: tmux
• Version: 2.1.49
• Feedback ID: c710b391-8ea9-47a0-8927-388cf21d8aef

Errors

[{"error":"Error: LSP server plugin:typescript-lsp:typescript failed to start: spawn typescript-language-server ENOENT\n    at Object.start (file:///Users/navi/.claude/local/node_modules/@anthropic-ai/claude-code/cli.js:2625:22369)\n    at process.processTicksAndRejections (node:internal/process/task_queues:105:5)\n    at async Object.H [as start] (file:///Users/navi/.claude/local/node_modules/@anthropic-ai/claude-code/cli.js:2625:24805)","timestamp":"2026-02-20T21:54:25.416Z"},{"error":"Error: spawn typescript-language-server ENOENT\n    at ChildProcess._handle.onexit (node:internal/child_process:285:19)\n    at onErrorNT (node:internal/child_process:483:16)\n    at process.processTicksAndRejections (node:internal/process/task_queues:90:21)","timestamp":"2026-02-20T21:54:25.416Z"},{"error":"Error: Failed to start LSP server plugin:typescript-lsp:typescript: spawn typescript-language-server ENOENT\n    at file:///Users/navi/.claude/local/node_modules/@anthropic-ai/claude-code/cli.js:2625:32664\n    at process.processTicksAndRejections (node:internal/process/task_queues:105:5)","timestamp":"2026-02-20T21:54:25.416Z"}]