Docs: add deno install instructions

[Ardakilic]

This PR introduces deno install instructions for OpenSpec.

I've tried already and I've been using without issues.

I've also added a small notice for @latest tag parsing.

Thanks!

Summary by CodeRabbit

• Documentation
  • Added a new Deno installation section to the documentation, including important notes on potential parsing issues with version tags and providing example installation commands with both flexible and version-pinned syntax options.

[coderabbitai]

📝 Walkthrough

Walkthrough

This PR adds a new Deno installation section to the installation documentation under Package Managers. The section includes guidance about potential parsing issues with the @latest tag and provides example deno install --global --allow-all commands, with an alternative version-pinned syntax for reproducibility.

Changes

Deno Installation Documentation

Layer / File(s)	Summary
Deno Installation Section docs/installation.md	New Deno subsection added under Package Managers with notes on @latest tag handling and example installation commands using deno install --global --allow-all, plus a version-pinned alternative.

Estimated code review effort

🎯 1 (Trivial) | ⏱️ ~3 minutes

Poem

🐰 A Deno path now shines so bright,
With install commands set just right,
Version pins to hold them steady,
Documentation now is ready!
✨

🚥 Pre-merge checks | ✅ 5

✅ Passed checks (5 passed)

Check name	Status	Explanation
Description Check	✅ Passed	Check skipped - CodeRabbit’s high-level summary is enabled.
Title check	✅ Passed	The title 'Docs: add deno install instructions' directly and clearly describes the main change: adding Deno installation instructions to the documentation.
Docstring Coverage	✅ Passed	No functions found in the changed files to evaluate docstring coverage. Skipping docstring coverage check.
Linked Issues check	✅ Passed	Check skipped because no linked issues were found for this pull request.
Out of Scope Changes check	✅ Passed	Check skipped because no linked issues were found for this pull request.

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✨ Finishing Touches

🧪 Generate unit tests (beta)

• Create PR with unit tests

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[coderabbitai]

Actionable comments posted: 2

🤖 Prompt for all review comments with AI agents

Verify each finding against current code. Fix only still-valid issues, skip the
rest with a brief reason, keep changes minimal, and validate.

Inline comments:
In `@docs/installation.md`:
- Around line 29-30: Rewrite the sentence to improve grammar and clarify the
logic: change "change `@latest` tag with" to "replace the `@latest` tag with", add
"the" before "@latest tag", and make the flow explicit by stating that if Deno
has trouble resolving `@latest` you should instead specify a concrete version (for
example replace the `@latest` tag with a version specifier like @^1.3.1). Ensure
the resulting sentence reads smoothly and unambiguously explains when and how to
use a pinned version.
- Around line 32-36: Replace the overly permissive Deno install commands that
use --allow-all with the minimal required permissions; update the bash snippets
that install npm:`@fission-ai/openspec` (both the `@latest` and @^1.3.1 variants) to
use --allow-read --allow-write --allow-env --allow-net instead of --allow-all so
the installation lines reflect only the actual permissions OpenSpec needs.

🪄 Autofix (Beta)

Fix all unresolved CodeRabbit comments on this PR:

• Push a commit to this branch (recommended)
• Create a new PR with the fixes

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ℹ️ Review info

⚙️ Run configuration

Configuration used: Path: .coderabbit.yaml

Review profile: CHILL

Plan: Pro

Run ID: 484f8d20-e2f2-4530-838a-c3e8dd8e98be

📥 Commits

Reviewing files that changed from the base of the PR and between 053d8a5 and b632401.

📒 Files selected for processing (1)

• docs/installation.md