fix(coding-agents): find Claude sessions for underscore paths (#3732)

* fix(coding-agents): find Claude sessions for underscore paths

* fix(coding-agents): encode every non-alphanumeric in the Claude project dir

Claude Code does not special-case underscores: it replaces EVERY
non-alphanumeric character in the absolute path with `-`. Encoding only
`/`, `.` and `_` still missed whole repositories, most commonly ones with
a space in the path (`~/Documents/My Projects/...`), which reported
"no past sessions found on disk" while the transcripts sat on disk under
their real name.

Verified against Claude Code 2.1.241 by running it in two directories:

    .../hs_under_test   -> ...-hs-under-test
    .../hs+odd@repo v2  -> ...-hs-odd-repo-v2

Case is preserved and runs are not collapsed, so the encoding is a 1:1
character substitution.

Widening the class cannot misattribute a session: the directory name only
narrows the candidate set, and each transcript must still record a `cwd`
inside the repository before it is imported. A regression test covers that
collision directly.

Claude-Session: https://claude.ai/code/session_01HVZ94d143NPSsZjbnvwqba

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Co-authored-by: Nicolò Boschi <boschi1997@gmail.com>