fix(core): enforce min_tool_version check during pack install

[breferrari]

Summary

• Packs can declare min_tool_version in their manifest to require a minimum weave version. Previously this field was parsed but never enforced, so incompatible packs would silently install and potentially break.
• Adds IncompatibleToolVersion error variant and a check_min_tool_version() function that compares pack.min_tool_version against CARGO_PKG_VERSION using semver comparison.
• Enforces the check in install_from_registry(), install_local() (both normal and dry-run paths), and use_profile::switch() so users always see a clear upgrade message.

Closes #197

Test plan

• Unit test: pack with min_tool_version higher than current returns IncompatibleToolVersion error
• Unit test: pack with min_tool_version equal to current succeeds
• Unit test: pack with no min_tool_version succeeds (backward compatible)
• E2E test: local pack with min_tool_version = "99.0.0" fails install with clear message
• cargo fmt --all passes
• cargo test --lib passes (215 tests, 0 failures)

[Copilot]

Pull request overview

This PR enforces min_tool_version from pack.toml so packs that require a newer weave version fail early with an actionable error, rather than installing and potentially breaking.

Changes:

• Adds a new WeaveError::IncompatibleToolVersion error variant for clear upgrade guidance.
• Introduces check_min_tool_version() (semver compare vs CARGO_PKG_VERSION) and calls it in registry installs, local installs (including dry-run), and profile switching.
• Adds unit tests for the version check and an E2E test covering an incompatible local pack.

Reviewed changes

Copilot reviewed 4 out of 4 changed files in this pull request and generated no comments.

File	Description
src/core/install.rs	Adds check_min_tool_version() and enforces it in install flows; includes unit tests.
src/core/use_profile.rs	Enforces min_tool_version during use_profile::switch() (dry-run and normal).
src/error.rs	Adds IncompatibleToolVersion error variant and message.
tests/e2e/cli_install.rs	Adds E2E coverage for local install failing on incompatible min_tool_version.