chore: prepare release v0.3.0 (#179)

## Summary

Prepare the workspace for the v0.3.0 release and make the release
workflow compatible with repository branch-creation rules.

- Bump all workspace crates and the internal `agentic-core` dependency
to `0.3.0`.
- Refresh `Cargo.lock`.
- Keep release commits, tags, and GitHub releases automated.
- Remove temporary release-branch creation and validation, which fails
under the repository's branch-creation restrictions.

After this PR is merged, publish `agentic-server-core` first, wait for
crates.io indexing, then publish `agentic-server`.

## Test Plan

- `cargo check --workspace`
- `cargo fmt --all -- --check`
- `cargo clippy --all-targets -- -D warnings`
- `cargo test` (all executed tests passed; 8 PostgreSQL integration
tests are ignored because `TEST_POSTGRES_URL` is not configured)

Signed-off-by: Francisco Javier Arceo <farceo@redhat.com>

chore: prepare release v0.3.0 (#179)

## Summary

Prepare the workspace for the v0.3.0 release and make the release
workflow compatible with repository branch-creation rules.

- Bump all workspace crates and the internal `agentic-core` dependency
to `0.3.0`.
- Refresh `Cargo.lock`.
- Keep release commits, tags, and GitHub releases automated.
- Remove temporary release-branch creation and validation, which fails
under the repository's branch-creation restrictions.

After this PR is merged, publish `agentic-server-core` first, wait for
crates.io indexing, then publish `agentic-server`.

## Test Plan

- `cargo check --workspace`
- `cargo fmt --all -- --check`
- `cargo clippy --all-targets -- -D warnings`
- `cargo test` (all executed tests passed; 8 PostgreSQL integration
tests are ignored because `TEST_POSTGRES_URL` is not configured)

Signed-off-by: Francisco Javier Arceo <farceo@redhat.com>