Problem: pressing `o`/`O` in a canola buffer placed the cursor at
column 0, requiring manual navigation past concealed ID prefixes and
column text (icons, permissions) to reach the name column.
Solution: add `show_insert_guide()` which temporarily sets
`virtualedit=all` on empty lines and positions the cursor at the
name column. Computes the correct virtual column by measuring the
visible column prefix width via `nvim_strwidth`, adjusting for
`conceallevel` (0=full ID width, 1=replacement char, 2/3=hidden).
Restores `virtualedit` on `TextChangedI` or `InsertLeave`.
Problem: the codebase still used the upstream \`oil\` naming everywhere —
URL schemes, the \`:Oil\` command, highlight groups, user events, module
paths, filetypes, buffer/window variables, LuaCATS type annotations,
vimdoc help tags, syntax groups, and internal identifiers.
Solution: mechanical rename of every reference. URL schemes now use
\`canola://\` (plus \`canola-ssh://\`, \`canola-s3://\`, \`canola-sss://\`,
\`canola-trash://\`, \`canola-test://\`). The \`:Canola\` command replaces
\`:Oil\`. All highlight groups, user events, augroups, namespaces,
filetypes, require paths, type annotations, help tags, and identifiers
follow suit. The \`upstream\` remote to \`stevearc/oil.nvim\` has been
removed and the \`vim.g.oil\` deprecation shim dropped.
