chore: add a make help target

[DevSolex]

Summary

Closes #160

Adds a help target to the Makefile that lists every available target with its one-line description. Makes help the default so running plain make with no arguments shows the usage guide instead of running the CI gate.

Changes

• help target: parses inline ## comments on each rule line using grep + awk and prints a formatted target/description table.
• .DEFAULT_GOAL := help: ensures make with no arguments runs help.
• Inline ## comments: moved each target's description from a standalone # comment above the rule to an inline ## comment on the rule line, keeping descriptions co-located with the targets they describe.

Output of make help / make:

Usage: make <target>

  all             Run fmt-check, lint, and test (CI gate).
  build           Native debug build.
  wasm            Optimised WASM artifact for deployment.
  test            Run the full test suite.
  fmt             Format the workspace in place.
  fmt-check       Verify formatting without modifying files (used in CI).
  lint            Lint every target and treat warnings as errors.
  audit           Audit dependencies for known vulnerabilities.
  clean           Remove build artifacts.
  deploy          Build, install, and deploy to testnet. Pass an identity: make deploy ID=alice
  help            Show this help message.

Acceptance criteria met

• make help lists the available targets with a one-line description each
• help is the default target when make is run with no arguments
• Descriptions stay in the Makefile next to the targets they describe

Verification

cargo fmt --check          ✓
cargo clippy --all-targets -- -D warnings  ✓
cargo test                 ✓  (109 tests passed)

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[Glittersup]

Please fix conflicts @DevSolex