feat: add cargo install filtering

[FlorianBruniaux]

Problem

cargo install outputs verbose compilation logs (dependency resolution, compiling N crates, warnings) when only the final "Installing/Installed/Replacing" lines matter for LLM context.

Evidence

rtk discover on 405 sessions (30 days) shows 53 occurrences of cargo install as the #2 unhandled command by count.

Command                  Count    Example
cargo install               53    cargo install --path . --force

Typical output is 50-200 lines of compilation noise for 2-3 useful lines.

Proposed behavior

rtk cargo install [args] should:

1. Execute cargo install [args] normally
2. Filter output to show only:
   • Installing / Installed / Replacing / Compiling rtk v... (the target crate only)
   • Errors and warnings from the target crate
   • Final status line
3. Strip all intermediate Compiling dependency_name v... lines
4. Preserve exit code

Example

Before (raw):

  Installing rtk v0.11.0
    Updating crates.io index
     Locking 130 packages to latest compatible versions
      Adding colored v2.2.0 (available: v3.1.1)
      Adding dirs v5.0.1 (available: v6.0.0)
      ... (50+ lines)
   Compiling proc-macro2 v1.0.70
   Compiling unicode-ident v1.0.12
   ... (100+ lines)
   Compiling rtk v0.11.0
    Finished release profile
   Replacing /Users/user/.cargo/bin/rtk
    Replaced package `rtk v0.9.4` with `rtk v0.11.0` (executable `rtk`)

After (rtk filtered):

  Installing rtk v0.11.0 (130 deps)
   Compiling rtk v0.11.0
    Replaced rtk v0.9.4 -> v0.11.0

Estimated savings: 80-90% token reduction.

Notes

This could be handled as a subcommand of the existing rtk cargo module, extending the match in cargo_cmd.rs (or equivalent) to intercept install alongside build, test, clippy, check.