Fix install.ps1 crash when piped through iex and render in PowerShell 5.1 - #2

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* Fix install.ps1 crash when piped through iex and render in PS 5.1

Three bugs surfaced by running the one-liner installer in stock Windows
PowerShell 5.1:

1. $PSScriptRoot is empty when the script is piped through Invoke-Expression
   (iwr ... | iex), so `Join-Path $PSScriptRoot 'rust\Cargo.toml'` threw
   'Cannot bind argument to parameter Path because it is an empty string'
   right after 'Building from source...'. Introduce a Get-LocalCheckoutDir
   helper that falls back to $PSCommandPath and $MyInvocation.MyCommand.Path
   and finally returns $null. The source-build branch now treats $null as
   'no local checkout' and skips straight to the user-scope git clone.

2. The backtick-e escape (`e) is only an ESC literal in PowerShell 6+.
   In Windows PowerShell 5.1 it's just the character 'e', which is why the
   user saw literal 'e[38;2;0;255;65m' in the output instead of green text.
   Replace with $ESC = [char]27 so ANSI sequences render on 5.1 too.

3. Box-drawing glyphs printed as '?' on the user's terminal because the
   default OEM code page can't represent them. Set [Console]::OutputEncoding
   to UTF-8 early in the script (wrapped in try/catch in case the host
   forbids it).

Co-Authored-By: jacob levesque <jaemlev@icloud.com>

* Check git fetch/reset exit codes in source-build fallback (cherry-picked from PR #2)

Co-Authored-By: jacob levesque <jaemlev@icloud.com>

* Windows audit, offline/proxy install support, clippy/fmt cleanup

Windows correctness fixes:
- platform::extra_path now adds \$USERPROFILE\.cargo\bin so freshly-installed Rust user binaries are discoverable.
- bash tool degrades to 'cmd /C' on Windows (no /bin/sh).
  Existing POSIX-only printf tests now gated to #[cfg(unix)].
- plugins/runtime hooks::shell_command: fix Windows mut warning, gate
  unused std::path::Path import.
- file_ops symlink test scoped under #[cfg(unix)] (Windows had unused let).

install.ps1 network-restricted / offline support:
- New flags: -OfflineSource, -OfflineZip, -Proxy,
  -ProxyUseDefaultCredentials, -Repo.
- Auto-detect HTTP_PROXY/HTTPS_PROXY env vars.
- Get-WebRequestSplat applies proxy + NTLM credentials uniformly to all
  Invoke-WebRequest calls (release zip, rustup-init, git fallback).
- Friendly error when Zscaler/raw.githubusercontent.com filtering hits,
  pointing user at -OfflineSource or -OfflineZip workflow.

Docs:
- New INSTALL.md: Linux/macOS quickstart, Windows quickstart, three
  network-restricted workflows (proxy, offline source, offline zip),
  troubleshooting, install locations.
- README points at INSTALL.md for restricted networks.
- .gitignore picks up .hackcode/, .hackcode-agents/, .hackcode-src/
  runtime artefacts so they don't get committed.

Rust workspace cleanup so cargo clippy --workspace --all-targets -- -D
warnings now passes clean on both Linux and x86_64-pc-windows-gnu:
- Workspace [lints.clippy] allows the pedantic / style lints that newer
  clippy releases (1.95+) added but that the existing codebase has many
  of (doc_markdown, match_same_arms, too_many_lines, uninlined_format_args,
  cast_possible_truncation, type_complexity, manual_split_once, etc.).
  Substantive lints (correctness, suspicious, perf) stay enforced.
- A handful of substantive fixes were applied directly rather than
  allow-listed: redundant pattern matching, identical match arms,
  doc-comment backticks, is_ok_and on a Result.
- cargo clippy --fix + scripts/fmt.sh swept the remaining cascade of
  formatting nits across crates touched by the lint changes.

Co-Authored-By: jacob levesque <jaemlev@icloud.com>

---------

Co-authored-by: Devin AI <158243242+devin-ai-integration[bot]@users.noreply.github.com>
Co-authored-by: jacob levesque <jaemlev@icloud.com>