feat: navigation core, remote parsing, layout and clone #1

Goal

gitcd clones a repository into a predictable path under root and the shell can jump to it.
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Context

• Trigger: first milestone of the tool, bootstrapped from the design below.
• Affected: the whole repository, which does not exist as code yet.

Design this milestone implements

Per host settings, with a default template for the rest:

root: ~/Code

layout:
  default: "{host}/{owner}/{repo}"

hosts:
  dev.azure.com:
    layout: "{host}/{org}/{project}/{repo}"
    aliases: [ssh.dev.azure.com, vs-ssh.visualstudio.com]
  github.com:
    aliases: [github-work, github-private]
    protocol: ssh

The alias map is not optional. Two GitHub accounts are driven by SSH host aliases, because
GitHub binds one SSH key to one account, so the parser sees github-work as the host. Without
the map the layout breaks for the case the tool exists for.

Accepted inputs: SSH URL, HTTPS URL, scp style git@host:owner/repo.git, the Azure DevOps
_git form, and the bare host/owner/repo shorthand. The host is lowercased at parse time.
{owner} accepts slashes, for GitLab subgroups.

The binary prints the resolved path on stdout and everything else on stderr, so a shell function
can wrap it. gitcd shell-init zsh|bash|fish prints that snippet and gitcd path <query> is the
plumbing command it calls.

House conventions

• cmd/gitcd/ holds flag parsing and dispatch only, logic in internal/<area>. No CLI
  framework, flag and hand written dispatch, as in release-me.
• Standard library plus gopkg.in/yaml.v3, the parser release-me already uses. Any other
  dependency needs a reason in the pull request.
• Apache-2.0 license header first in every .go file.
• mise.toml pins every tool, Taskfile.yaml holds one target per check, check aggregates
  and holds no command of its own, CI runs one job per target.

Acceptance criteria

• Repository scaffolding exists: AGENTS.md, CLAUDE.md holding @AGENTS.md, README.md,
  LICENSE, mise.toml, Taskfile.yaml, .golangci.yaml, .goreleaser.yaml,
  renovate.json, .editorconfig, .gitignore, .github/workflows/, .agent-skills.json.
• docs/concepts/gitcd.md records problem, goals, non goals, approach, alternatives and open
  questions, carried over from the bootstrap plan.
• internal/remote parses all five input forms into host, owner, project and repo, resolves
  host aliases, and lowercases the host. One test per form.
• internal/layout renders a template to a path and maps a path back to a remote.
• internal/config loads ~/.gitcd.yaml, falls back to $XDG_CONFIG_HOME/gitcd/config.yaml,
  applies defaults and rejects an unknown key with a named error.
• gitcd clone <url|shorthand> clones into the rendered path and prints that path on stdout.
• gitcd clone is idempotent: a target that exists with the same remote prints the path and
  exits 0, and a target that exists with a different remote fails with both remotes named.
• gitcd path <query> resolves an exact repository name or a host/owner/repo to its path.
• gitcd shell-init zsh|bash|fish prints a working wrapper function.
• gitcd version prints the version, set at build time.
• Every command supports --dry-run where it writes.
• Tests build git repositories under a temporary directory with GIT_CONFIG_GLOBAL,
  GIT_CONFIG_NOSYSTEM=1 and a controlled HOME. No network.
• task check passes.
• The bootstrap PLAN.md is deleted, its content now living in this issue series and in
  docs/concepts/gitcd.md.

Out of scope

• Profiles, identity and anything writing git config. That is the next milestone.
• list, cd, fuzzy matching, doctor, adopt, status, sync.
• The landing page at gitcd.ostendorf.cloud.

Open question to resolve while implementing

• Azure DevOps SSH remotes are assumed to use host ssh.dev.azure.com with path
  v3/{org}/{project}/{repo}, and HTTPS dev.azure.com/{org}/{project}/_git/{repo}. Unverified.
  Confirm against a real remote before fixing the parser's behaviour.