fix(pager): use temp file and TTY for interactive pagers like most

[syf2211]

Summary

Fixes glow -p failing when PAGER is set to interactive pagers like most that reject piped stdin.

Motivation

glow -p previously piped rendered markdown directly to the pager process stdin. Pagers such as most expect a file path argument and read keyboard input from the controlling terminal, so they exit with status 1 (#153).

Changes

• Add runPagerCommand() that writes rendered output to a private temp file and passes the file path to the configured pager
• Attach /dev/tty (or CONIN$ on Windows) for pager keyboard input
• Include pager stderr in failure messages for easier diagnosis (complements include pager stderr in --pager failure messages #948)

Tests

• go test ./... — all pass
• Added pager unit tests covering temp-file handoff, pager flags, empty content, and stderr error propagation

Notes

• Supersedes the diagnostic-only approach in include pager stderr in --pager failure messages #948 by fixing the underlying most compatibility issue while keeping improved error messages.
• Large documents incur a brief temp-file write; this matches common pager integrations (man, git, etc.).

Fixes #153