fix: better help for user without mise installs

[janderssonse]

Pull Request Description

The bug this started from

devbase-check runs linters via command -v . That trusts whatever's on PATH. The trap: if .mise.toml pins something
like pipx:reuse but pipx isn't installed on the host, mise install silently skips that pin. The linter then either finds a
stale system copy of reuse (wrong version, different behaviour) or fails with an opaque "not found". Nothing tells the user
the real cause is a half-done mise install.

So the theme of this branch is: mise is the source of truth for tool versions, and if mise says a pin is missing, we say so
— loudly, once, and with a clear way out.

What a user sees now

Running just lint-all with any pinned tool missing prints one message:

✗ mise install is incomplete — run: mise install
- pipx:reuse
(to skip: --ignore-missing-linters or DEVBASE_CHECK_IGNORE_MISSING_LINTERS=1)

Not once per linter — once, from a preflight at the top of verify.sh. Each linter still has its own guard, but when it fires
for a tool that isn't its own (e.g. running ./linters/license.sh while aqua:mvdan/sh is missing), it stays quiet — reuse
isn't broken, no point complaining.

If the user passes --ignore-missing-linters (or sets DEVBASE_CHECK_IGNORE_MISSING_LINTERS=1), the preflight warns and
proceeds; affected linters emit a skip marker so the summary table shows them as - with mise pin missing, instead of wrongly
passing because a stray binary was on PATH. For locked-down environments where mise install genuinely can't complete,
DEVBASE_CHECK_ALLOW_SYSTEM_TOOLS=1 disables the whole check.

Example illustrating how different features of this works in different scenarios:

Checklist

• Changes are limited to a single goal (avoid scope creep)
• I confirm that I have read any Contribution and Development guidelines (CONTRIBUTING and DEVELOPMENT) and are following their suggestions.
• I confirm that I wrote and/or have the right to submit the contents of my Pull Request, by agreeing to the Developer Certificate of Origin, (adding a 'sign-off' to my commits).