chore: migrate project template to Miden v0.16

[Keinberger]

Overview

This PR synchronizes the standalone project-template code with the Miden v0.16 template rendered from 0xMiden/compiler@next at 52abe7d76d5757dae3ca074b16a3cea361fa5a4e. The seven .claude/skills files are intentionally excluded and are handled in stacked draft PR #64.

Key Changes

• matches the compiler template across all 27 non-skill template paths, subject only to the documented CI compatibility correction below
• uses the stable miden = "0.14" guest SDK and miden-sdk-build-script-support = "0.14"
• retains the two upstream build.rs files that prepare the package cache for ordinary Cargo and IDE builds
• intentionally keeps contract Cargo.lock files absent, matching the compiler template policy for these standalone library crates, while retaining the root workspace lockfile
• preserves the v0.16 counter component, note, integration helper, binary, and integration test behavior
• installs the stable 0.16.0 toolchain through midenup in CI

Compiler Template Parity

The rendered compiler workflow invokes midenc --version directly and exports MIDENUP_HOME. GitHub Actions proved two midenup 1.0 integration problems with those exact lines: midenc is exposed through the miden dispatcher, and exporting MIDENUP_HOME makes the unchanged helper select miden build, which now dispatches to midenc rather than cargo-miden and therefore fails to build the contract Cargo manifest.

This PR keeps the upstream helper unchanged and applies only the workflow correction: verify with miden midenc --version, add the active toolchain opt directory to GITHUB_PATH, and let the helper use its existing cargo miden fallback.

Skills Follow-up

Issue #63 tracks the v0.16 skills migration. Draft PR #64 is stacked on this branch and sources the six shared skills from 0xMiden/agent-tools#17, with the project-only miden-client-cli skill migrated separately.

Tests

Both contracts build with cargo-miden 0.10.0, and the integration suite passes with exactly one counter_test, zero failures, and zero ignored tests. GitHub CI passed end to end in run 33879688492, including the contract rebuilds performed by the integration test.