feat(monorepo): cross-package dependency bump propagation

[BryanFRD]

Problem

`workspace.dependsOn` triggers a downstream bump when an upstream package is bumped, but `src/monorepo/run/mod.rs:535-617` always emits a patch, regardless of the upstream bump type:

```rust
compute_next_version(.., BumpType::Patch, strategy) // line ~568
```

That means: if `@scope/core` goes `1.x → 2.0.0` (breaking), `@scope/cli` which depends on it gets a `patch` bump — even though `cli` is now compiling against a breaking new `core` API. End users upgrade `cli` thinking it's a patch and break in prod.

Also, the dependency version range declared in `package.json` / `Cargo.toml` peer maps is never rewritten — consumers continue pinning the old range.

Comparison

• changesets propagates the bump type and offers `updateInternalDependencies: "patch"|"minor"` to tune.
• release-please does manifest-level cascade with the same bump type.

Proposal

1. Track the bump type of upstream packages and propagate it. Default: `major-on-major` (only major cascades).
2. Optional `workspace.update_dependents: true` that, when bumping pkg `B`, rewrites version constraints in `A`'s manifest where `A.dependsOn = ["B"]`.
3. Config shape:
   ```toml
   [[package]]
   depends_on = [{ name = "core", propagate = "major-on-major" }]
   ```

Test plan

• Fixture: `feat!:` on B with A depending on B → A gets major.
• Fixture: `update_dependents = true` rewrites `A/package.json` deps.